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Robotic Spacecraft (Astronomy, Planetary, Earth, Solar/Heliophysics) => Mars Science Laboratory (MSL) and Mars 2020 Rover Section => Topic started by: mmeijeri on 08/16/2009 10:27 PM

Title: Mars EDL technologies
Post by: mmeijeri on 08/16/2009 10:27 PM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 08/16/2009 10:37 PM
SDLVs and other HLV concepts are sometimes advocated because large payload fairings are useful for large aeroshells, which would allow you to land sizeable payloads on Mars. One obvious alternative would be propulsive braking and descent. This would be expensive, but so are HLVs, especially if you have to carry fixed costs for 20 years before you get any benefit.

One big problem with propulsive braking is that the Martian atmosphere gets in the way. It's very difficult to fire a rocket engine into a hypersonic airstream. It depends at least on Mach number and if I'm not mistaken Mach 2-3 is believed to be possible for final propulsive descent. I wonder what other factors affect this. I imagine dynamic pressure has something to do with it. Would it be a problem to go faster than Mach 3 100km up where the resulting dynamic pressure could be less than 1 Pa? It's hard to imagine that would be a problem, but then again these things are not always intuitive.

One scheme would be to brake to a standstill above the atmosphere, but as low as possible, and then descend as fast as is possible without exceeding the Mach number/density/dynamic pressure/whatever envelope that would preclude further propulsive braking. The slower you have to go, the higher the gravity losses of course. I imagine some hybrid of propulsive braking and aerobraking could be best for architectures that don't have HLVs.
Title: Re: Mars EDL technologies
Post by: Kaputnik on 08/16/2009 10:51 PM
Not sure this thread is in the right place, unless we're staying specifically on the topic of how Mars EDLS affects launcher choice.

To that end, I would suggest that the situation is as follows:

a) We choose to extrapolate existing EDLS to the larger size needed to support a manned mission. As a rough guide this allows an entry vehicle mass of 150kg per square metre of heatshield area. This density can increase if a lifting entry is used.
Some example of entry mass according to PLF size, without accounting for lifting entry:
5m (current EELV)= 3t
7.5m (Phase 2 EELV; NSC)= 6.6t
8.4m (Smallest inline SDLVs; upgraded NSC)= 8.3t
10m (Ares V; Standard hammerhead Jupiter)= 11.8t
12m (larger hammerhead SDLVs)= 17t
15m (largest possible SDLV?)= 26.5t

This choice very clearly favours larger PLFs and really mandates an SDLV solution, or a radical new wide-core EELV.

b) We choose to save money on the launcher and instead pour it into advanced EDLS such as propulsive braking, hypersonic drag devices, folding heatshield, inflatable heatshields, biconic or lifting body designs, etc.

There are strong arguments either way, but IMHO we have the opportunity to develop an SDLV today that could easily give us 12m+ PLFs, and that seems to be just about on the cusp of allowing us to land big enough payloads to support a manned mission- especially if a lifting entry is used, increasing the above numbers.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 08/17/2009 08:20 PM
This article gives a summary of Mars Exploration Entry, Descent and Landing Challenges (http://www.4frontierscorp.com/dev/assets/Braun_Paper_on_Mars_EDL.pdf).
Title: Re: Mars EDL technologies
Post by: Nathan on 08/22/2009 12:33 PM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Since we can do 2.5 tonne chunks already with viking technology then lets just land stuff on mars in 2.5 tonne chunks. Lots of launches but mass produced entry shells help lower costs.
Transit habitat can be bigger since it doesn't land. Crew lands in rover to take them to inflatable habitat, spare rover, greenhouse, etc all landed in 2.5 tonnes chunks. (actually 2.5 tonnes at entry interface so ~1.5 tonnes payload.)
Title: Re: Mars EDL technologies
Post by: simon-th on 08/22/2009 12:45 PM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Since we can do 2.5 tonne chunks already with viking technology then lets just land stuff on mars in 2.5 tonne chunks. Lots of launches but mass produced entry shells help lower costs.
Transit habitat can be bigger since it doesn't land. Crew lands in rover to take them to inflatable habitat, spare rover, greenhouse, etc all landed in 2.5 tonnes chunks. (actually 2.5 tonnes at entry interface so ~1.5 tonnes payload.)

2.5mt is not enough as the smallest chunk.

But still, if you really want to go with the smallest possible piece to land on Mars, use the current upper boundary with (enhanced) Viking technology heatshields. That's about 3-4mt at 5.5m (Ariane 5) and maybe about 5mt with a potential Delta IV Heavy hammerhead 6-7m fairing.
Title: Re: Mars EDL technologies
Post by: simon-th on 08/22/2009 12:48 PM

There are strong arguments either way, but IMHO we have the opportunity to develop an SDLV today that could easily give us 12m+ PLFs, and that seems to be just about on the cusp of allowing us to land big enough payloads to support a manned mission- especially if a lifting entry is used, increasing the above numbers.

I think your option b. makes more sense.

12m PLFs aren't near enough for the Mars mission surface payloads required if you go for traditional reentry. Let's not now start to limit our potential Mars mission 30 years out by the potential PLF diameter and thus design the payloads around the launch vehicle fairings. Rather come up with a creative solution (e.g. simple folding techniques for heatshields) down the line which make much more sense.
Title: Re: Mars EDL technologies
Post by: Nathan on 08/23/2009 12:41 AM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Since we can do 2.5 tonne chunks already with viking technology then lets just land stuff on mars in 2.5 tonne chunks. Lots of launches but mass produced entry shells help lower costs.
Transit habitat can be bigger since it doesn't land. Crew lands in rover to take them to inflatable habitat, spare rover, greenhouse, etc all landed in 2.5 tonnes chunks. (actually 2.5 tonnes at entry interface so ~1.5 tonnes payload.)

2.5mt is not enough as the smallest chunk.

But still, if you really want to go with the smallest possible piece to land on Mars, use the current upper boundary with (enhanced) Viking technology heatshields. That's about 3-4mt at 5.5m (Ariane 5) and maybe about 5mt with a potential Delta IV Heavy hammerhead 6-7m fairing.
The 4.6m diameter MSL entry vehicle masses 2.8tonnes at entry interface. 4.6m fits within a 5m launch shroud with proper clearances.
If this vehicle was allowed to fall to -2km altitude (isidis etc) then ~1tonne useful payload can be delivered to the surface.
If we mass produce aeroshells at this size we can drop 1tonne rovers, greenhouses, supply modules, etc. Crew would land in a 1 tonne rover and drive to and link up with one or two 1 tonne resource trailer/s then move on to locate a 1 tonne inflatable habitat (linking up the resource trailer for life support & power). Crew would then drive to locate a second rover, resource trailer and greenhouse module.
Rovers would be remote controllable to enable rescue.

A mars transit module would provide habitation, consumables and emergency consumables for the trip out and is not restricted to the ~2.5 tonne mass limit.

In all one would expect around 10 entry vehicles per launch window to provide redundancy. 1-2 crew of course landing in the rover. More than that is unrealistic.
A falcon 9 heavy could send 3 aeroshells per launch. Or 1 aeroshell/rover plus transit habitat.
Launching 3 falcon heavies per launch window would do the job.

May want 2 rover/hab launches per mission - 1 crew member on each. Lonely trip out but happy days when meet up again on surface.

Ballistic coefficient max for 4.6 m aeroshell is 153kg/m2 which can handle 3 tonnes at entry so a bit more mass to surface may be possible. Key is to land at low elevations and have redundancy.

If you use existing technology.
Title: Re: Mars EDL technologies
Post by: Nathan on 08/23/2009 12:51 AM
Actually probably only two aeroshells per falcon 9 heavy if given a departure c3 of 10kg2/m2.
Title: Re: Mars EDL technologies
Post by: Nathan on 08/24/2009 09:04 AM
Actually you're - we'd need more than that. Probably double each landing.
Title: Re: Mars EDL technologies
Post by: savuporo on 08/24/2009 09:39 AM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Since we can do 2.5 tonne chunks already with viking technology then lets just land stuff on mars in 2.5 tonne chunks. Lots of launches but mass produced entry shells help lower costs.
Transit habitat can be bigger since it doesn't land. Crew lands in rover to take them to inflatable habitat, spare rover, greenhouse, etc all landed in 2.5 tonnes chunks. (actually 2.5 tonnes at entry interface so ~1.5 tonnes payload.)

2.5mt is not enough as the smallest chunk.
.. because ?
Title: Re: Mars EDL technologies
Post by: Nathan on 08/25/2009 09:11 AM
A new thread for discussing Mars EDL technologies and especially how they might impact the choice of architecture, launchers and in-space transportation.
Since we can do 2.5 tonne chunks already with viking technology then lets just land stuff on mars in 2.5 tonne chunks. Lots of launches but mass produced entry shells help lower costs.
Transit habitat can be bigger since it doesn't land. Crew lands in rover to take them to inflatable habitat, spare rover, greenhouse, etc all landed in 2.5 tonnes chunks. (actually 2.5 tonnes at entry interface so ~1.5 tonnes payload.)

2.5mt is not enough as the smallest chunk.
.. because ?

I get why he says that. It's tight. 2.5tonnes leads to ~1tonne on the surface.
People weigh 100kgs each, space suit and food for say 30 days ~150kgs.
Leaves 750kgs for pressurised rover.
Doable. Rover does not need recycling life support tech. Just basic tech with perhaps water recovery.
Resource modules & other entry pods would contain long duration items.
That is doable.
Needs a very basic rover though.
If the upper aeroshell can be used as the rover's pressurised hull then we may be able to use more of that 2.5 tonne entry mass.

Tight but doable. More would be better but if that is all there is then so be it.
Title: Re: Mars EDL technologies
Post by: simon-th on 08/25/2009 10:26 AM

I get why he says that. It's tight. 2.5tonnes leads to ~1tonne on the surface.
People weigh 100kgs each, space suit and food for say 30 days ~150kgs.
Leaves 750kgs for pressurised rover.

So, your proposal is to encapsule each Mars surface mission crew member separately in a rover and without a spacesuit (estimate about 250kg for crew person + spacesuit and other individual life support equipment), 15kg per day per person in provisions. That says you can't do it in 2.5mt chunks - even if those chunks were the net payload to the Martian surface because A. you will get all your crew members to the Martian surface in one piece and B. your pressurized rover is going to weight a lot more than 750kg (the power source alone, e.g. RTGs for the rover will weight more than that).
Title: Re: Mars EDL technologies
Post by: Nathan on 08/25/2009 10:35 AM

I get why he says that. It's tight. 2.5tonnes leads to ~1tonne on the surface.
People weigh 100kgs each, space suit and food for say 30 days ~150kgs.
Leaves 750kgs for pressurised rover.

So, your proposal is to encapsule each Mars surface mission crew member separately in a rover and without a spacesuit (estimate about 250kg for crew person + spacesuit and other individual life support equipment), 15kg per day per person in provisions. That says you can't do it in 2.5mt chunks - even if those chunks were the net payload to the Martian surface because A. you will get all your crew members to the Martian surface in one piece and B. your pressurized rover is going to weight a lot more than 750kg (the power source alone, e.g. RTGs for the rover will weight more than that).

Crew member including spacesuit & food. =250kg. It takes far less than 15kg per day per person. 2.5kg max. So that's 20 days of food.
Rover would use solar power not rtg. Apollo LRV had a mass of 210kg. Add thin pressurised enclosure and solar panels (batteries already included but become rechargeable). As mentioned one may be able to use the entry mass of the upper aeroshell as part of the rover hull? Alternatively just use steel or kevlar.No airlock. Whole rover depressurises.

Obviously not talking about returning to Earth at any point. Just land near prepositioned equipment in simple mobile vehicle.
Title: Re: Mars EDL technologies
Post by: simon-th on 08/25/2009 11:17 AM

Crew member including spacesuit & food. =250kg. It takes far less than 15kg per day per person. 2.5kg max. So that's 20 days of food.

No. We know from the ISS that you have to calculate about 15kg per day per person - with water recycling that goes down, but obviously your simple Mars rover won't have that.

250kg is for the crew member + spacesuit + individual life support equipment.

Quote
Rover would use solar power not rtg.
That doesn't work. The solar cell area you require for a pressurized rover (about 5-10kWe constant) is much too high to attach to a rover. All studies have RTGs for rovers as front runners with rechargeable/re-fuelable pressurized rovers as a second alternative (rover gets fueled/charged at base, goes for a ride, comes back and gets fueled/charged again - from an immobile station).

P.S. RTGs are actually the most mass efficient way to power a rover - batteries or fuel cells or the in-workable (from an area perspective) solar cells are more massive.

 
Quote
Apollo LRV had a mass of 210kg. Add thin pressurised enclosure and solar panels (batteries already included but become rechargeable). As mentioned one may be able to use the entry mass of the upper aeroshell as part of the rover hull? Alternatively just use steel or kevlar.No airlock. Whole rover depressurises.

Those are all non-workable ideas. All pressurized rover designs mass way above the Apollo LRV. We are talking several mt here, even without an airlock.

For a simple overview of a 20-day autonomous 2-crew Mars rover design proposal from 1997 look here: http://www.astronautix.com/craft/drmrized.htm (http://www.astronautix.com/craft/drmrized.htm). It clocks in at 16.5mt. The best suitable power source with 1.1mt are RTGs, the photo-voltaic alternative would mass 2.8mt and require an area of 1300m² at 66m³ packaging.

[/quote]
Title: Re: Mars EDL technologies
Post by: Nathan on 08/25/2009 11:43 AM

Crew member including spacesuit & food. =250kg. It takes far less than 15kg per day per person. 2.5kg max. So that's 20 days of food.

No. We know from the ISS that you have to calculate about 15kg per day per person - with water recycling that goes down, but obviously your simple Mars rover won't have that.

250kg is for the crew member + spacesuit + individual life support equipment.

Quote
Rover would use solar power not rtg.
That doesn't work. The solar cell area you require for a pressurized rover (about 5-10kWe constant) is much too high to attach to a rover. All studies have RTGs for rovers as front runners with rechargeable/re-fuelable pressurized rovers as a second alternative (rover gets fueled/charged at base, goes for a ride, comes back and gets fueled/charged again - from an immobile station).

P.S. RTGs are actually the most mass efficient way to power a rover - batteries or fuel cells or the in-workable (from an area perspective) solar cells are more massive.

 
Quote
Apollo LRV had a mass of 210kg. Add thin pressurised enclosure and solar panels (batteries already included but become rechargeable). As mentioned one may be able to use the entry mass of the upper aeroshell as part of the rover hull? Alternatively just use steel or kevlar.No airlock. Whole rover depressurises.

Those are all non-workable ideas. All pressurized rover designs mass way above the Apollo LRV. We are talking several mt here, even without an airlock.

For a simple overview of a 20-day autonomous 2-crew Mars rover design proposal from 1997 look here: http://www.astronautix.com/craft/drmrized.htm (http://www.astronautix.com/craft/drmrized.htm). It clocks in at 16.5mt. The best suitable power source with 1.1mt are RTGs, the photo-voltaic alternative would mass 2.8mt and require an area of 1300m² at 66m³ packaging.

[/quote]

Ok so need a bigger chunk? Life support may be big issue then- depends on how easy water recycling can be. Urine processing and air dehumidification is thus a must.
I guess with the rover I am think of something along the lines of the 1.4tonne rover from Zubrin's Case for Mars book only lighter, slower, less capable. Something between Apollo LRV and the Zubrin rover. The rover you are referencing is for long duration missions of 500km range. I'm only needing for running about the landing site area ~ten k on so.
Again one needs to consider how basic the rover can be. It's a tent with wheels. Hell, Spacesuit technology could provide life support.
Title: Re: Mars EDL technologies
Post by: simon-th on 08/25/2009 12:04 PM

Ok so need a bigger chunk? Life support may be big issue then- depends on how easy water recycling can be. Urine processing and air dehumidification is thus a must.
I guess with the rover I am think of something along the lines of the 1.4tonne rover from Zubrin's Case for Mars book only lighter, slower, less capable. Something between Apollo LRV and the Zubrin rover. The rover you are referencing is for long duration missions of 500km range. I'm only needing for running about the landing site area ~ten k on so.

I am not saying the rover needs to be 16mt. What I am saying is that 1mt in a shell with a person in it won't work. 5mt - ok, might work for 2 crew, 10mt-15mt for the whole crew of 4-6.

Quote
Again one needs to consider how basic the rover can be. It's a tent with wheels. Hell, Spacesuit technology could provide life support.

That would basically require that your astronauts descent to the Martian surface in the heat shield inside only protected by a. a tent or b. their spacesuits. Not viable for NASA for safety reasons - not even considering that your heatshield shell gets discarded down the line and you would expose your crew members in spacesuits to the atmosphere while still at high speeds.
Title: Re: Mars EDL technologies
Post by: savuporo on 08/25/2009 08:33 PM
Quote
Rover would use solar power not rtg.
That doesn't work. The solar cell area you require for a pressurized rover (about 5-10kWe constant) is much too high to attach to a rover.
Something doesnt compute. Tesla 52 KWh integrated ESS with battery pack weighs 400kg ( with ~200kw output ). And these are not best of the available batteries anymore.
At 10KW draw, thats enough juice for 5 hours. 5 hours should be enough to cover any landing ellipse and get to prelanded station/charging point.
Title: Re: Mars EDL technologies
Post by: savuporo on 08/25/2009 08:42 PM
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.

Again, i dont see why 1 ton landed is not enough for anything ?
Title: Re: Mars EDL technologies
Post by: A_M_Swallow on 08/25/2009 10:04 PM
On Mars the rover could have a chemical engine.  Use CO2 as the oxidizer.  The fuel could be magnesium or one of the alkali metals.  Burn in a heat engine and generator.  Use electricity to drive the wheel motors.

p.s.  An atmospheric oxidizer means that neither LOX nor lots of batteries needs bringing from Earth, saving mass.
Title: Re: Mars EDL technologies
Post by: Kaputnik on 08/25/2009 10:04 PM
MSL won't use PVAs s I'm not sure where you're trying to go with that one.

Realistically, nobody is going to Mars unless they can get home again. That means that the smallest possible cargo size is the ascent vehicle.

In an ideal world we would land an all-up, ready-fuelled vehicle, ready to go. That allows a crew return to orbit at any time, not subject to any assembly or other operations.
Second best is to land the vehicle dry, with an onboard ISRU plant including power supply. This provides a ready-to-go vehicle subject only to a waiting period for the ISRU operation.
Third best is to start offloading the power supply and/or the ISRU plant. This means that you need some basic assembly- linking up of fluid transfer lines, power supply etc.
IMHO going any further than that would become completely impracticable. You'd have to start splitting the vehicle up into chunks, and require the crew to link these together 'in the field'. Nobody builds rockets that way on Earth, why presume it would work on Mars?
Title: Re: Mars EDL technologies
Post by: A_M_Swallow on 08/25/2009 11:09 PM
{snip}
IMHO going any further than that would become completely impracticable. You'd have to start splitting the vehicle up into chunks, and require the crew to link these together 'in the field'. Nobody builds rockets that way on Earth, why presume it would work on Mars?

Simple, we do not know any other way of getting the mass of the ascent stage down to 2500 kg.
Title: Re: Mars EDL technologies
Post by: randomly on 08/26/2009 01:42 AM
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.

Take a look at the MER data for why solar cells on Mars are less than ideal. Although the rover arrays could produce over 900W peak under ideal conditions the rovers got stranded for up to 5 months at a time waiting on enough power to move. Dust accumulation on the panels is only part of the problem, the planet wide dust storms which can last several months can reduce the opacity of the atmosphere down to 1%. Even under ideal conditions you only get about 25% of the power per day due to the day/night cycle, atmospheric absorbption, and sun angle.

I would be much more comfortable with an RTG augmented with some batteriers.
Lithium batteries only work well in a fairly limited temperature range. Not only do you have to keep them warm enough when they are not in use but you need systems to remove substantial amount of heat when they are suppling power and charging. All those systems( you have to accurately monitor every single cell volt in the pack) , insulation, mounting etc. that's suitable for a space based environment means you won't get close to the energy density of the basic cells.  You'd be doing very well to get 50 wh/kg. As a reference the lithium batteries on the Mars rovers are 280 Whr and weight 9 Kg, or about 30 Wh/kg.

Unfortunately battery technology improves only slowly.
Title: Re: Mars EDL technologies
Post by: savuporo on 08/26/2009 06:58 AM
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.

Take a look at the MER data for why solar cells on Mars are less than ideal. Although the rover arrays could produce over 900W peak under ideal conditions the rovers got stranded for up to 5 months at a time waiting on enough power to move. Dust accumulation on the panels is only part of the problem, the planet wide dust storms which can last several months can reduce the opacity of the atmosphere down to 1%. Even under ideal conditions you only get about 25% of the power per day due to the day/night cycle, atmospheric absorbption, and sun angle.

I would be much more comfortable with an RTG augmented with some batteriers.
"Comfortable" is not an engineering unit.

I was making a simple point, if you need your landed 1 mt chunks to make rendezvous with prelanded hab/base/gear in the landing ellipse, you can do it with precharged battery-powered mobile equipment.

You would only need stationary solar arrays on site ( again prelanded ) to recharge the batteries later to make other uses of the vehicles.
Title: Re: Mars EDL technologies
Post by: simon-th on 08/26/2009 09:10 AM

I was making a simple point, if you need your landed 1 mt chunks to make rendezvous with prelanded hab/base/gear in the landing ellipse, you can do it with precharged battery-powered mobile equipment.


It's a very risky approach to land people in a rover (let's say a 3mt rover with one crew and charged batteries), if your batteries run out in a couple of hours and you need to get to your base to recharge the rover. What, if your rover after landing is stuck and you need to do an EVA to free it? What if you encounter a problem while on route to the base? Of course in that case the astronaut could try to reach the base on foot. But is that really acceptable from a safety point of view?

We should be realistic here. There is no way a Mars mission would send each crewmember to Mars separately on a separate pressurized rover only to fulfill some ridiculous "small chunk to surface" requirement. From an engineering standpoint it makes just a lot more sense to increase the payload to surface mass per unit. And you do that by increasing the heatshield diameter - something which isn't a showstopper, a technology just needs to be developed that helps you with very large heat shields (e.g. folding the Mars descent heat shield or going for supplemental inflatable heatshield extensions or breaking into low Martian orbit first or using going for a more powered descent in the second phase of the descent etc.). Reasonably we should talk about a Mars surface mission with at least ~25mt chunks to the surface.
Title: Re: Mars EDL technologies
Post by: savuporo on 08/26/2009 07:29 PM

I was making a simple point, if you need your landed 1 mt chunks to make rendezvous with prelanded hab/base/gear in the landing ellipse, you can do it with precharged battery-powered mobile equipment.


It's a very risky approach to land people in a rover (let's say a 3mt rover with one crew and charged batteries), if your batteries run out in a couple of hours and you need to get to your base to recharge the rover. What, if your rover after landing is stuck and you need to do an EVA to free it? What if you encounter a problem while on route to the base? Of course in that case the astronaut could try to reach the base on foot. But is that really acceptable from a safety point of view?

From safety point of view, going to Mars is a risky business this way or another. What if your RTG behemoth dies ? What if your big heatshield burns up ? etc etc.
Batteries and electric motors are fairly mundane, predictable and well understood technologies, that have been used on mars and space applications since.. forever.
You would try aim for as small landing ellipses as possible anyway. You could have astronaut walk to the base if the distance is tolerable, you could have a pre-landed backup remote control rover charged at the base for contingencies. There are ways to mitigate _any_ risk.

Quote
We should be realistic here. There is no way a Mars mission would send each crewmember to Mars separately on a separate pressurized rover only to fulfill some ridiculous "small chunk to surface" requirement.
Yes we should be realistic, and live within our means. If we have capability to launch 20mt chunks to orbit, then lets use it to build the exploration program. If we have capability to land only 1mt at a time on mars with technology at hand, then design with that.

What is ridiculous is this tendency to dismiss anything non-conventional, not involving big-bucks and big rockets approaches, as not viable.

Its entirely plausible that the first people to land on mars will not be paid by public, but by private money, and the risks that such crew would be willing to take would be entirely different from your line of thinking.
Title: Re: Mars EDL technologies
Post by: rklaehn on 08/26/2009 07:48 PM
Yes we should be realistic, and live within our means. If we have capability to launch 20mt chunks to orbit, then lets use it to build the exploration program. If we have capability to land only 1mt at a time on mars with technology at hand, then design with that.

Some new technology development will be required for a manned mars mission. And I think it is much easier to develop technology to land bigger chunks on mars than to try to build a manned mars mission from 1t pieces. The optimum is probably somewhere above 20t.

Quote
Its entirely plausible that the first people to land on mars will not be paid by public, but by private money, and the risks that such crew would be willing to take would be entirely different from your line of thinking.

Indeed. But a company such as bigelow aerospace that is specialized in large inflatable structures would probably just design a big inflatable heat shield rather than trying to squeeze a manned mission into 1t pieces.
Title: Re: Mars EDL technologies
Post by: Nathan on 08/28/2009 09:52 PM
{snip}
IMHO going any further than that would become completely impracticable. You'd have to start splitting the vehicle up into chunks, and require the crew to link these together 'in the field'. Nobody builds rockets that way on Earth, why presume it would work on Mars?

Simple, we do not know any other way of getting the mass of the ascent stage down to 2500 kg.

yeah this would be one way only with constant resupply.
Title: Re: Mars EDL technologies
Post by: Nathan on 08/28/2009 10:01 PM
Another alternative: in the australian ASTRONOMY Magazine there was a story that said that Braun & co say that with an inflatable supersonic decelerator replacing the parachute that landing masses of 15 tonnes would be practical. (20 tonnes at entry interface)

I like this idea as launching 20 tonne chunks is certainly more practical and could use the HLV shuttle derived vehicle without suborbital staging. The EDS could simply send the crew in one launch seated in a 15 tonne rover. The could meet up with a 15 tonnes habitat &resource module. Then launch to orbit in a 15 tonne ascent vehicle that used martian resources. An Earth return vehicle would be waiting in orbit to bring crew and samples home.

Landing ten 15 tonne chunks on the surface would build up a base very quickly and allow a greater range of exploration and capabilities. Plus the crew size could build up. Plus extra redundancy.
Title: Re: Mars EDL technologies
Post by: Xentry on 08/28/2009 10:38 PM
Another alternative: in the australian ASTRONOMY Magazine there was a story that said that Braun & co say that with an inflatable supersonic decelerator replacing the parachute that landing masses of 15 tonnes would be practical. (20 tonnes at entry interface)

Well, quoting directly from the Braun paper summarizing the Mars EDL challenges and the corresponding viable solutions, "a 30 m, Mach 3 parachute allows for a subsonic propulsive deceleration maneuver if entry masses are below approximately 33 t".

Of course, you'd need to qualify a parachute to open at Mach 3, but again quoting from the same source, from all the possible solutions - inflatable hypersonic decelerators, supersonic propulsive descent, re-qualification of parachutes, etc - "It is likely that the parachute Mach and diameter option will be exercised first as these require extension of existing qualified technology".

One might as well take the cue and assume a 30t entry vehicle with a 30m, Mach 3-qualified parachute as a reference. And, of course, propulsive descent from Mach 0.8 downwards. Problem solved.  8)
Title: Re: Mars EDL technologies
Post by: simon-th on 08/28/2009 10:43 PM
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.

Again, i dont see why 1 ton landed is not enough for anything ?

Please for instance read the link I provided when talking about minimal mass rover designs for Mars.

Again, the area that needs to be covered with solar cells is so wide, you could never attach these solar cells to the Mars rover in order to use it as a mobile source of power.

What you of course can do is get an immobile solar cell power station to Mars and then recharge your batteries at that station.

The link I provided has RTGs at 1.1mt mass and a photo-voltaic solution at 2.8mt (batteries + solar cells + equipment to make that work + additional heating equipment required (you get heating from your RTGs "for free"...)). So, you might get your mass of your photo-voltaic solution down a bit, maybe to 2mt with modern solar cells (that work in space) and better batteries, maybe even down further. But they will never match RTGs in mass efficiency or packaging efficiency (m³ required). And unlike RTGs, your solar cell solution will always require your rover to be dependent on recharging at an immobile about 1200m² wide solar power station.
Title: Re: Mars EDL technologies
Post by: DLR on 09/01/2009 06:17 AM
One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested.

Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.
Title: Re: Mars EDL technologies
Post by: Xentry on 09/01/2009 02:49 PM
One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested.

Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.
NASA will likely re-qualify their Viking parachutes for a wider flight envelope (larger diameter and deployment at higher Mach numbers) before researching and developing an almost entirely new technology (even though inflatable heat shields are hugely promising for both planetary and Earth applications). Since it is likely that by using these improved parachutes they'll be able to land >30t on Mars, inflatable heat shields will probably have to wait.   :(
Title: Re: Mars EDL technologies
Post by: DLR on 09/02/2009 03:07 AM
But then you still need HLVs with 10m fairings ... unless you go for some sort of lifting body design, which may be a bit tricky ... since you would enter the atmosphere "head first", slow down, deploy your chute, turn around, fire your engines. With blunt decelerators the vehicle always faces in the "correct" direction for reentry, parachute deployment as well as rocket motor deceleration.
Title: Re: Mars EDL technologies
Post by: simon-th on 09/02/2009 07:49 AM
One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested.

Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.
NASA will likely re-qualify their Viking parachutes for a wider flight envelope (larger diameter and deployment at higher Mach numbers) before researching and developing an almost entirely new technology (even though inflatable heat shields are hugely promising for both planetary and Earth applications). Since it is likely that by using these improved parachutes they'll be able to land >30t on Mars, inflatable heat shields will probably have to wait.   :(

Whatever works is good enough. We don't need to go "exotic" just for the sake of doing it. If conventional, proven technology works, then we should use it. However, absent technology development of a folding technique (or inflatable heat shield add-ons) for Viking-shaped heatshields and parachute technique, we ain't going to see >30mt to the Martian surface.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 07:52 AM
Whatever works is good enough. We don't need to go "exotic" just for the sake of doing it. If conventional, proven technology works, then we should use it. However, absent technology development of a folding technique (or inflatable heat shield add-ons) for Viking-shaped heatshields and parachute technique, we ain't going to see >30mt to the Martian surface.

There's still powered descent or a hybrid approach.
Title: Re: Mars EDL technologies
Post by: kraisee on 09/02/2009 08:22 AM
I'm personally convinced that a combination of these technologies is going to be required.

A human crew is going to need to land in some sort of rover, probably a pressurized one -- which means some pretty serious mass.

I believe that a 10m PLF will be needed in order to contain the lander plus a simply enormous inflatable heatshield -- something in the order of 30-50m diameter.

After 'entry', the heatshield & PLF would be jettisoned and a set of extremely large parachutes will create sufficient drag to bring the spacecraft safely down to within a few hundred feet of the surface, and finally the landing will be performed by active thrusters of some sort, under pilot-control to help avoid bad ground.   The suspension of the rover should absorb the final 'touchdown' stresses.

I don't see many ways to reduce the mass of the total system while increasing the mass of the final delivered 'module'.


What I'm most interested in currently, is seeing what 'abort' capabilities might be designed into this solution.   There is a very wide trade space there.

Ross.
Title: Re: Mars EDL technologies
Post by: simon-th on 09/02/2009 08:51 AM

I believe that a 10m PLF will be needed in order to contain the lander plus a simply enormous inflatable heatshield -- something in the order of 30-50m diameter.


You don't need 50m diameter heatshields (I am not even talking about the structural problems you get into by using a 50m heat-shield...). 15-25m does perfectly well. And even for the unreasonably-sized 50m inflatable (or foldable) heath-shield, you don't require a 10m PLF. A 20m heat-shield folded up fits perfectly well into a 6m PLF.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 09/02/2009 09:12 AM
Ross, you haven't been reading our posts over at MarsDrive, have you?

One of the options that we're looking at is a big methane/LOX fuel-cell powered "mobile hab". Using a conventional 10 or 12m heatshield we're able to deliver between 12 and 19 tonnes to the surface. This mobile hab would be landed with the crew and a large amount of methane/LOX fuel to provide significant range. We're looking at at least 2000km intial driving range. That should be plenty enough to get you to the MAV (for refueling or an abort) in even the worst-case (high landing-error) scenarios. Furthermore, the extra fuel you need for driving might be able to be used for the purpose of a purely propulsive descent in the event of a parachute failure or the like. So its a bit of a win-win in terms of safety.

Also it just so happens that the byproduct of methane/LOX reacting in the fuel-cell is lots of water. We can use this 'free' water to supplement the crews consumables requirement (which is up to 90% water, I believe). That is probably a significant enabler of the whole mobile hab concept.

There is even the option of pre-caching smaller 'supply packs' in orbit the window before crew launch. A 4.5m aeroshell pack could deliver about two tonnes of supplies to the surface. That is small enough to be launched on a variety of international or commercial LVs. These packs would provide 'anywhere, anytime' delivery of critical supplies or even spare parts; being pin-point landed right next to wherever the mobile habs happen to be. That sort of system would vastly increase the safety of the whole mission. You can even use this 'orbital caching' system to deliver non-critical 'nice to have' items like big drills 'on demand and on location'. Both of these systems take the load off of the mobile hab and enable vastly increased field science capability as well as increased safety.

We might even look at abort-to-surface options on the mars ascent vehicle. If we design the ascent capsule with abort-to-surface systems designed for the more difficult martian reentry environment then perhaps that same design might work well enough to be used for the less-difficult earth reentry too. If that is the case you can conceivably use your mars ascent vehicle as your crew reentry vehicle. That would increase the requirements on your in-situ propellant production system (as the heavier crew capsule) but it takes mass off of your return vehicle, as it no longer has to lug your earth reentry capsule all the way from earth to mars and then back. Perhaps we're on to something with that.

What are your thoughts guys?

Anyway you're welcome to check out the discussion at: http://tech.groups.yahoo.com/group/marsdrivemission/

You can find a few teaser shots of the mobile hab concept there too: http://groups.yahoo.com/group/marsdrivemission/attachments/folder/0/list

- Mike

Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 09:49 AM
Here's a link to a recent master's thesis on propulsive descent:

Fully-Propulsive Mars Atmospheric Transit Strategies for High-Mass Missions (http://www.ssdl.gatech.edu/Papers/Masters/CMarsh_8900.pdf).

I haven't read all of it yet, but I agree with the general direction. The author considers depots in LEO and LMO. It would work even better with additional depots at L1, SEL2 and Sun Mars L1/L2 and with ISRU and SEP.
Title: Re: Mars EDL technologies
Post by: Archibald on 09/02/2009 10:23 AM
Quote
It would work even better with additional depots at L1, SEL2 / ISRU and SEP

Yes ! I like this. Ammonia, hydrogen and/or hydrazine (or any other nitrogen - hydrogen coumpound usable as rocket fuel, if someone know another, plesae tell me...) allows to combine these three elements.

To summarize: a EML-1 or -2 ammonia/hydrogen/hydrazine depot refuel an arcjet-tug for Earth departure. The said arcjet-tug is refueled through ISRU at Mars, for the return trip. 
Thus you combine electric propulsion (low IMLEO) with ISRU (low IMLEO) into an ultra-low IMLEO Mars expedition.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 10:31 AM
And initially you wouldn't even need cryogenic depots, although you would want to take advantage of them as soon as they become available. ISRU would require new technology (especially on Phobos/Deimos, less so on Mars itself) but everything else is high TRL proven technology.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 11:11 AM
Another link, co-authored by the ubiquitous professor Braun:

Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars Entry, Descent, and Landing (http://www.ssdl.gatech.edu/Papers/Technical%20Papers/AIAA-2009-5613.pdf).
Title: Re: Mars EDL technologies
Post by: DLR on 09/02/2009 11:36 AM
May I ask, why would you want to use rocket propulsion for hypersonic/supersonic braking manouevres when you can just resort to larger shroud diameters?

Perhaps that's why we should get a HLV. It certainly makes things a lot easier for Mars. For the Moon it's not necessary, but for Mars, I certainly think so.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 11:43 AM
Precisely so you don't need an HLV. And apparently Mars EDL is a problem anyway, even with large fairings, hence Braun & co's research into supersonic retropropulsion.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 11:47 AM
How much easier do things become if you 1) enter from orbit instead of directly, 2) slow down more than is necessary to enter the atmosphere, 3) use the biggest possible EELV fairing (6.5m) and 4) use a lifting body? I'm thinking of entering the atmosphere at a mere 2km/s.

And then there's always the brute-force approach of coming to a standstill above the atmosphere and then descending as rapidly as dynamic pressure, Mach number and whatever other parameters are relevant will allow.
Title: Re: Mars EDL technologies
Post by: DLR on 09/02/2009 12:04 PM
A problem? I thought flying a 30t lander on a lifting trajectory with a 15m heatshield would get you below Mach 0.8 at sufficient altitude to start retropropulsion.

The last approach is just plain nuts, no offense.  :D ;)

The vehicle would mass hundreds of tonnes and would only be able to land tens of tonnes.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:05 PM
How much easier do things become if you 1) enter from orbit instead of directly, 2) slow down more than is necessary to enter the atmosphere, 3) use the biggest possible EELV fairing (6.5m) and 4) use a lifting body? I'm thinking of entering the atmosphere at a mere 2km/s.

I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

A lifting body or any kind of high L/D shape would be very useful to reduce the required propulsive delta-v. But then a non-axially symmetric vehicle might be much harder to design. It might be easier to just accept the 0.2 PMF required for semi-propulsive braking.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:08 PM
May I ask, why would you want to use rocket propulsion for hypersonic/supersonic braking manouevres when you can just resort to larger shroud diameters?

Perhaps that's why we should get a HLV. It certainly makes things a lot easier for Mars. For the Moon it's not necessary, but for Mars, I certainly think so.

We won't get a HLV. So we can either do lots of idle speculation about what we could do with an HLV, or we can try to deal with reality. I prefer the latter.

Besides, even if sufficient funds were available for a HLV, I would prefer this money to be spent on actual in-space R&D and hardware.
Title: Re: Mars EDL technologies
Post by: DLR on 09/02/2009 12:13 PM
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:20 PM
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.

Just saying it does not make it so.

A manned mars mission could be done using existing launchers and propellant depots. Take the mars direct mission architecture: the biggest piece is about 30t. There is no need for anything bigger than that.
Title: Re: Mars EDL technologies
Post by: simon-th on 09/02/2009 12:22 PM
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

It is possible to climb to up to ~50km with airships in Earth's atmosphere. Considering that the mean atmospheric pressure on Mars is about as much as at ~30km height on Earth, but due to the lower gravity on Mars the atmosphere actually reaches higher up, I think it is worth at least considering.

Of course, this approach requires a. breaking into low Mars orbit first b. extending the airship and filling it up with a gas (probably hydrogen) c. requires some kind of ion engine for slow deceleration until friction from the Martian atmosphere provides said deceleration.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 12:23 PM
A problem? I thought flying a 30t lander on a lifting trajectory with a 15m heatshield would get you below Mach 0.8 at sufficient altitude to start retropropulsion.

The last approach is just plain nuts, no offense.  :D ;)

Now, now, no need for strong language. What I described is most certainly not nuts, it is a perfectly feasible approach if you want to exclude HLV, as I do.

Quote
The vehicle would mass hundreds of tonnes and would only be able to land tens of tonnes.

Not hundreds, a bit over one hundred.
Title: Re: Mars EDL technologies
Post by: DLR on 09/02/2009 12:25 PM
But when you slow down from orbit and at the sime time attempt to maitain your altitude above the surface you're incurring huge gravity losses.

Not to speak about assembling this massive vehicle in space and launching it towards Mars and then braking into on orbit.

I'd rather put my money on a HLV than that scheme.  ;)
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 12:26 PM
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.

Quote
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.

Quote
A lifting body or any kind of high L/D shape would be very useful to reduce the required propulsive delta-v. But then a non-axially symmetric vehicle might be much harder to design. It might be easier to just accept the 0.2 PMF required for semi-propulsive braking.
Title: Re: Mars EDL technologies
Post by: simon-th on 09/02/2009 12:28 PM
Well then deal with the reality of not going to Mars.

Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.

An HLV will very likely be used for a mission to Mars, but from a mission point of view, nothing on the technical side says you can't go with a mission based on Atlas V Phase 1 (40mt) or even with current launchers, both augmented with fuel depots. A 40mt partially dry-launched EDS can be easily filled up with enough propellant on orbit to launch a 40mt payload launched on a second rocket and docked with the EDS to Mars.

Alternatively, you go for the "all-in" variety of doing a Mars mission and assemble your Mars ship in LEO altogether. 1. Launch depots 2. launch fuel to depots 3. launch Mars surface payload 4. launch dry EDS 5. lauch hab module and 6. launch the crew. Join things together, fill up the dry EDS stage(s) and off you go. All with EELVs. That requires a lot of launches (about 40-50 times 25mt launchers or about 25 if you go for Atlas V Phase 1 if you go for chemical propulsion) but it is possible.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:30 PM
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

I think the airship to orbit idea of JP aerospace is completely unworkable. But the idea of using large inflatable structures for reentry is quite workable.

Here is a very interesting project of the german mars society about mars reentry using a balloon that is inflated in space. It is made from somewhat heat-resistant material, and due to the large surface area per mass unit (low ballistic coefficient), the heating is gentle enough for the balloon to survive reentry.

http://www.archimedes-ballon.de/index.php?id=EN (http://www.archimedes-ballon.de/index.php?id=EN)
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:39 PM
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.

Rockets work just fine when firing into a supersonic flow. For example the separation rockets of the shuttle SRBs. You just have to make sure that the exit plane pressure of the rocket is significantly higher than the stagnation pressure of the supersonic flow.

Quote
Quote
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.

Yes. But the part where the thin atmosphere hurts you the most is not the initial part of the deceleration but the last part of the deceleration. Getting from 6km/s to 2km/s is no problem even with a high ballistic coefficient and the thin martian atmosphere. The part from 2km/s to subsonic is where you need the low ballistic coefficient and/or propulsive braking.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 12:40 PM
But when you slow down from orbit and at the sime time attempt to maitain your altitude above the surface you're incurring huge gravity losses.

Sure, the trick would be to descend as quickly as possible. If you descend too quickly you'll get into the velocity/altitude regime where you can no longer start your engine. You also have to take your T/W ratio into account, since you would want to come to a standstill above the surface, not below it... Apparently firing into a Mach 5-6 airstream is possible, but I would think that high up in the atmosphere, where density and dynamic pressure are very low, you might be able to go even faster than that.

So in the all-propulsive scenario you would initially brake to a standstill at an altitude of about 150 km, then plummet down to 20-30 km keeping your velocity below Mach 5-6, then slow down in the increasingly dense atmosphere to keep within the envelope where you can fire your thrusters and then slow down rapidly from around 10 km. I did some simple experiments with the Orbiter space simulator and it looked possible. Not easy but possible. Orbiter doesn't model the interaction between the thruster and an opposing hypersonic airstream, but it does model dynamic pressure. I would love to know what the maximum allowed dynamic pressure/Mach number/whatever envelope is.

My guess is that the all-propulsive approach while possible might be less effective than a hybrid. I'm thinking a hybrid would be best if you exclude HLV.

BTW I'm not denying a large fairing is an advantage for SDLV from the point of view of EDL. I'm just pointing out there appear to be good alternatives (and plenty of problems even with large fairings) so I have no reason to switch away from my preference of smaller launchers.
Title: Re: Mars EDL technologies
Post by: simon-th on 09/02/2009 12:46 PM
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.

I think the airship to orbit idea of JP aerospace is completely unworkable. But the idea of using large inflatable structures for reentry is quite workable.

Here is a very interesting project of the german mars society about mars reentry using a balloon that is inflated in space. It is made from somewhat heat-resistant material, and due to the large surface area per mass unit (low ballistic coefficient), the heating is gentle enough for the balloon to survive reentry.

http://www.archimedes-ballon.de/index.php?id=EN (http://www.archimedes-ballon.de/index.php?id=EN)

Thanks for the link. Basically this is what I meant - some kind of combination of aero-braking and use of buoyancy. The project website seems to be a bit dated (they speak of a launch this year...) but it quite interesting.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 12:56 PM
http://www.archimedes-ballon.de/index.php?id=EN (http://www.archimedes-ballon.de/index.php?id=EN)

Thanks for the link. Basically this is what I meant - some kind of combination of aero-braking and use of buoyancy. The project website seems to be a bit dated (they speak of a launch this year...) but it quite interesting.

They are going to be a secondary payload on the AMSAT P5A (http://www.amsat-dl.org/p5a/) mission, which is going to be a secondary payload on an ariane V launch.

I am not sure if they are going to make the launch window this year. But this is not just another powerpoint project: they have built working models and even flown a suborbital test flight.
Title: Re: Mars EDL technologies
Post by: Xentry on 09/02/2009 01:11 PM
But then you still need HLVs with 10m fairings ... unless you go for some sort of lifting body design, which may be a bit tricky ... since you would enter the atmosphere "head first", slow down, deploy your chute, turn around, fire your engines. With blunt decelerators the vehicle always faces in the "correct" direction for reentry, parachute deployment as well as rocket motor deceleration.
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others. And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.
As for lifting bodies, the parachute attachment point could also be located near the nose of the vehicle so it rotated the vehicle to the proper position for thruster firing right from the chute deployment moment. Not that I would advocate a lifting body for a manned Mars mission...
Title: Re: Mars EDL technologies
Post by: Xentry on 09/02/2009 01:13 PM
Whatever works is good enough. We don't need to go "exotic" just for the sake of doing it. If conventional, proven technology works, then we should use it. However, absent technology development of a folding technique (or inflatable heat shield add-ons) for Viking-shaped heatshields and parachute technique, we ain't going to see >30mt to the Martian surface.

There's still powered descent or a hybrid approach.
There is no other way than a hybrid approach. The chutes would have to be too big and heavy to allow a soft landing under a parachute.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 01:22 PM
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others.

Horizontal landers don't need large fairings. Habitats don't strictly need them either, look at the ISS. Inflatable habs sound more practical though.

Quote
And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.

Could EELV Phase 1 have 10m fairings? Current EELVs could support 6.5m, but I vaguely remember Crawley saying something about even Atlas Phase 3 having smaller fairings than an SDLV.
Title: Re: Mars EDL technologies
Post by: Xentry on 09/02/2009 01:39 PM
The need for 10m (and bigger) fairings is also driven by the lander stage and the habitat module dimensions, among others.

Horizontal landers don't need large fairings. Habitats don't strictly need them either, look at the ISS. Inflatable habs sound more practical though.

Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.


Quote
And to be honest, HLVs with 10m fairings sound like a pretty standard configuration to me.

Could EELV Phase 1 have 10m fairings? Current EELVs could support 6.5m, but I vaguely remember Crawley saying something about even Atlas Phase 3 having smaller fairings than an SDLV.

My view is that you'll either have HLV or you can forget about Mars. Also I think that despite the problems NASA is facing right now there will be an HLV.
I respect your point of view, but I think that it greatly complicates an already technically difficult mission to make (meaning, you'd need to add technology development costs that you wouldn't need in case you had an HLV, to the point where avoiding to build an HLV would be unreasonable).
In any case the Atlas Phase 3 would apparently have a cryogenic upper stage 7m in diameter, on top of which one could eventually imagine a ~10m fairing could be placed.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 01:47 PM
Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.

I wonder if that's true. Such a lander could be single stage, which would be a simplification. And initially it wouldn't have to do true landings, assuming the Deep Space option is chosen. What would make a horizontal lander difficult to design?

Quote
My view is that you'll either have HLV or you can forget about Mars.

Why is that?

Quote
Also I think that despite the problems NASA is facing right now there will be an HLV.
I respect your point of view, but I think that it greatly complicates an already technically difficult mission to make (meaning, you'd need to add technology development costs that you wouldn't need in case you had an HLV, to the point where avoiding to build an HLV would be unreasonable).

Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated. Hypergolic in-flight refueling is a proven technology and it's good enough for the foreseeable future.

Quote
In any case the Atlas Phase 3 would apparently have a cryogenic upper stage 7m in diameter, on top of which one could eventually imagine a ~10m fairing could be placed.

To be honest I'm not at all enthusiastic about anything bigger than EELV Phase 1, since it is hard to imagine how that could lead to a high flight-rate.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 02:09 PM
Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated.

At least according to the paper (http://www.ssdl.gatech.edu/Papers/Technical%20Papers/AIAA-2009-5613.pdf) you linked, this is the case. From the concluding remarks:

These conditions generally imply SRP initiation at the minimum altitude boundary defined by the timeline considerations of the subsequent EDL events.
You want to fire your supersonic retro propulsion as late as possible.

For the same ΔV, lower thrust coefficients are preferable as they preserve more aerodynamic drag. Overall, however, a lower initiation velocity is preferable over a lower CT.
If I read it correctly, CT is the ratio of propulsive force and aerodynamic force during the propulsive phase of reentry. So the conclusion is that you want your vehicle to have a large T/W and to do the propulsive braking as late as possible.

This can also be seen from the table on page 9, where the "delayed initiation" case with the highest T/W has by far the lowest PMF of 0.202.
Title: Re: Mars EDL technologies
Post by: simcosmos on 09/02/2009 02:11 PM

You don't need 50m diameter heatshields (I am not even talking about the structural problems you get into by using a 50m heat-shield...). 15-25m does perfectly well. And even for the unreasonably-sized 50m inflatable (or foldable) heath-shield, you don't require a 10m PLF. A 20m heat-shield folded up fits perfectly well into a 6m PLF.

simon-th, do you have a reference or a visual representation about such 20m diameter heat shield properly folded to fit inside a 6m diameter envelope?


I have made some very rough 'studies' about how to integrate a conceptual heat shield that could be folded in two main parts and the very preliminary results - under constraints also dependent of specific heat shield shape, while taking in account PLF width plus some free distance between payload and internal PLF walls - was  something more or less like:

a)   7.6m (external) diameter PLF: ~11.76m heat shield diameter
b) 10.0m (external) diameter PLF: ~15.56m heat shield diameter

There could exist better ways of folding the shield (again, dependent of its geometry): on the examples above was only trying to study something with the minimum of possible of parts for a rigid heat shield (which would have to be unfolded and integrated with payload + departure stage at LEO).

António
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 02:20 PM
So the conclusion is that you want your vehicle to have a large T/W and to do the propulsive braking as late as possible.

If firing into the hypersonic airstream is not the problem I thought it was, then I agree completely. The whole thing about braking outside the atmosphere and descending as quickly as possible was meant to avoid problems with hypersonic airstreams while keeping gravity losses as low as possible. If that's not an issue, then as close to a Hohmann transfer as possible would be best, which would mean high T/W and firing as late as possible. More realistically it would mean a gravity turn at as low an altitude and velocity as you could afford.
Title: Re: Mars EDL technologies
Post by: Xentry on 09/02/2009 02:23 PM
Well, then you'd have to build a new type of lander which you haven't done before. Hey I'm all for it, in fact I think it's the most practical solution, but it would sure add to the development costs. As a lifting body would.

I wonder if that's true. Such a lander could be single stage, which would be a simplification. And initially it wouldn't have to do true landings, assuming the Deep Space option is chosen. What would make a horizontal lander difficult to design?
If what's true? That you'd add to the development costs in case you were to develop a horizontal lander w.r.t. a been-there-done-that vertical lander? Ok, sure, you're entitled to that. I don't think it's difficult to design, just that it's a new type of vehicle and that historically speaking, new things cost more than replicas of old things.

My view is that you'll either have HLV or you can forget about Mars.

Why is that?
The reason was explained in the same post, in the very sequence of my claim. Implies the development of additional technologies (lifting body, inflatable heat shield and habitat modules, horizontal lander, etc) w.r.t. to an HLV-based Mars Mission.


Well, I certainly respect your point of view too, but I don't see how not having HLV complicates things very much. Propulsive braking might be expensive (much less so if rklaehn is right it's the last 2 km/s that is the problem), but not complicated. Hypergolic in-flight refueling is a proven technology and it's good enough for the foreseeable future.

Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.
Heat shield dimensions are a problem, and parachute dimensions are a problem. And the path of least resistance, according to Braun and Co. is re-qualifying the Viking parachutes and assuming an increased heat shield diameter (to 10-15m). It's their point of view.

To be honest I'm not at all enthusiastic about anything bigger than EELV Phase 1, since it is hard to imagine how that could lead to a high flight-rate.
I certainly agree that an HLV will have comparatively higher costs due to the lower flight rate as compared to smaller vehicles. Having a small fairing, however, does impact the technologies you're able to use for Mars EDL, and those you need to develop.
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 06:00 PM
Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.

In the table 6 "SRP Performance for 5 t Robotic Cases." in the paper (http://www.ssdl.gatech.edu/Papers/Technical%20Papers/AIAA-2009-5613.pdf) linked by mmeijeri, the initiation M∞ is between 2.96 and 1.82.

The M∞ is the mach number at initiation of the supersonic retro propulsion. Even in the case with the highest T/W, the initiation mach number is well above one.

Just for those who do not want to read the paper in detail: the proposed configuration uses a reentry shape similar to the mars science laboratory (MSL) with a diameter of 4.5m and very low-performance (but reliable) hydrazine monopropellant propulsion. It manages to land 5t on mars using between 1.0t and 1.5t of propellant depending on T/W.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 06:05 PM
I don't understand how a delta-v of 2km/s can lead to a mass fraction of 0.2. That's about what I'd expect with the vertical descent option using hypergolics. Surely it has to be better than that? Or is this comparing landed mass to IMLEO?
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/02/2009 06:09 PM
I don't understand how a delta-v of 2km/s can lead to a mass fraction of 0.2. That's about what I'd expect with the vertical descent option using hypergolics.

In the paper the proposed propellant is monopropellant hydrazine with an Isp of 225s. And 0.2 means that with an initial mass of 1ton, 200kg have to be propellant (the rest is structure and payload). For such a low-performance propellant that is not that bad.

Edit: I think the term propellant mass fraction is a bit confusing since people often use payload mass fraction and abbreviate it to PMF.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/02/2009 06:20 PM
Ah yes, that makes sense.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 09/03/2009 09:10 AM
Not to speak about assembling this massive vehicle in space and launching it towards Mars and then braking into on orbit.

Nope, it will easily fit inside an EELV fairing.

Quote
I'd rather put my money on a HLV than that scheme.  ;)

You seem to have a love for HLV. Note that it would be mostly other people's money going towards your hobby.
Title: Re: Mars EDL technologies
Post by: DLR on 09/03/2009 09:46 AM
I have a love for HLVs?  ;D

Remember that I was the guy who said it was perfectly feasible to fly cheap Lunar missions with ELVs, Soyuz and EML-1 staging.

But I'm not dogmatic about it. I think that for Mars missions a HLV is going to be the best solution.

Also I don't why MLVs shouldn't be incrementally updated until they basically become HLVs, for example like the Atlas with its "Phases".
Title: Re: Mars EDL technologies
Post by: Xentry on 09/06/2009 01:19 PM
Propulsive braking is not a problem, it just has to be accounted for. You also don't need to brake all the way from 2km/s (about Mach 6), just from Mach 0.8 according to Braun.

In the table 6 "SRP Performance for 5 t Robotic Cases." in the paper (http://www.ssdl.gatech.edu/Papers/Technical%20Papers/AIAA-2009-5613.pdf) linked by mmeijeri, the initiation M∞ is between 2.96 and 1.82.

The M∞ is the mach number at initiation of the supersonic retro propulsion. Even in the case with the highest T/W, the initiation mach number is well above one.

Just for those who do not want to read the paper in detail: the proposed configuration uses a reentry shape similar to the mars science laboratory (MSL) with a diameter of 4.5m and very low-performance (but reliable) hydrazine monopropellant propulsion. It manages to land 5t on mars using between 1.0t and 1.5t of propellant depending on T/W.

Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

I was taking the results from an earlier, less focused paper in which all different Mars EDL technology options were on the table, which is also linked to in this very thread - http://forum.nasaspaceflight.com/index.php?topic=18387.msg460969#msg460969

Here's the link to that paper: http://www.4frontierscorp.com/dev/assets/Braun_Paper_on_Mars_EDL.pdf
Title: Re: Mars EDL technologies
Post by: rklaehn on 09/06/2009 01:56 PM
Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

No, of course not.

I know that the standard approach is to use various aerodynamic devices such as supersonic parachutes to decelerate to subsonic speeds. I just think that the supersonic retropropulsion option is very attractive.

You need rocket propulsion in any case for a soft landing. So why not use it earlier and accept a bit lower mass fraction. You can use much higher ballistic coefficients, and you do not need something like 30m diameter supersonic parachutes.
Title: Re: Mars EDL technologies
Post by: Xentry on 09/07/2009 11:44 AM
Ok, but is an initiation Mach number over 1 really surprising for a paper which title is "Performance Characterization of Supersonic Retropropulsion for Application to High-Mass Mars EDL"?

No, of course not.

I know that the standard approach is to use various aerodynamic devices such as supersonic parachutes to decelerate to subsonic speeds. I just think that the supersonic retropropulsion option is very attractive.

You need rocket propulsion in any case for a soft landing. So why not use it earlier and accept a bit lower mass fraction. You can use much higher ballistic coefficients, and you do not need something like 30m diameter supersonic parachutes.

I agree - since you already have to have a propulsive landing, it makes every sense to explore supersonic retropropulsion. I was merely pointing out the perspective of the experts on the shortest path to making a manned Mars EDL possible.

Actually, in general I really don't care about which technology or strategy one uses, as long as it makes sense and makes things possible, as opposed to elaborating some grand scheme involving either a huge, multi-decadal development which will never happen and/or radical new technology (and launchers) which will almost surely cost billions which space agencies do not have (or, better yet, billions that the governments behind those agencies will never provide - not that they shouldn't, but as things are today, they just won't).

What strikes me the most as somewhat of a nonsense nowadays, is it seems as if it's the private companies led by space enthusiasts (Bigelow,SpaceX,Scaled Composites) which are developing the kind of new technology (inflatable modules for space stations and surface habitats, reusable launchers, cheap + frequent access to space) that's going to be needed to move any of those grand plans forward. It's pretty weird to think that space agencies, and NASA in particular, have failed miserably at what they should do best, which is developing the kind of enabling technologies that enable space exploration at an affordable cost.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 09/09/2009 04:18 AM
Hey guys.

I was wondering whether anyone has thought about putting some degree of abort-to-surface capability in the mars ascent capsule?

Because this is Mars, and the atmosphere is thin, I was thinking you could make the ascent capsule reallly wide and fat, but bare-boned and lightweight: Essentially extremely low-density. That way you might be able to get away with just a thin coating of PICA, and less descent propellant but huge parachutes instead. Land the thing on some giant air-bags or something. You could also use the ascent capsule as your earth-reentry capsule. That way you don't have to lug your reentry capsule all the way from earth to mars and then back again with your ERV (or MDS or transhab or whatever you want to call it).

Okay, full abort-to-surface capability might be a bit much. And you have the problem of saving the crews once they land hundreds of kilometers down-range (although this is where orbital caching of emergency supply packs can really help). So how about just a partial abort-to-surface capability: Fly a dog-leg ascent profile, and keeping the low-density capsule idea, allow an abort-to-surface during the vertical part of the ascent only. The capsule should fall nearer where they lifted off, and the sub-orbital reentry environment should be benign enough that you can keep the capsule really lightweight.

So there are two ideas here: 1) Put full EDL systems on your ascent capsule so you can use it as your earth-reentry capsule too. That way you have full abort-to-surface capability, and you don't have to lug your reentry capsule all the way from earth to mars and then back again.

And 2) Using a dog-leg ascent profile, and just putting a minimal abort-to-surface capability in the capsule to allow aborts during the vertical part of the descent only.

Both using extremely low-density capsule designs with big parachutes and minimal-mass landing systems.

Your thoughts guys?

I guess the question for (1) is: Can mars-optimized EDL systems be made to work adequately during earth-reentry (or vice-versa, whichever way you want to look at it). In other words, can you design an EDL system which can accomplish both tasks reasonably well, without resorting to complete duplication of systems?

And for (2): How lightweight can you make the capsule if you only design in abort-to-surface capability during the vertical part of ascent? And would the vertical flight phase last long enough to make a minimal abort-to-surface capability worthwhile?

- Mike
Title: Re: Mars EDL technologies
Post by: Lobo on 09/09/2009 10:45 PM
One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested.

Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.

Inflatable heat shield?  Sweet!  It’ll be just like Indiana Jones and the Temple of Doom, when they jumped out of the airplane with the inflatable raft!

But seriously, it’d be something to look at if there was anyway to do it to save mass.  I am assuming the huge inflatable heat shield would slow the craft enough that it wouldn’t see the temperatures during normal entry?  Normally that’d get hot enough to burn up anything inflatable, right?  I’m curious about that.

Perhaps instead of a “heat shield” you have a huge inflatable parachute that you deploy before entry.  More of an inflatable structure that would deploy the canopy when there’s otherwise no atmosphere yet to do it.  Then as you enter the atmosphere, that big inflatable parachute begins to gently create drag and slow the craft before it gets down into the thicker atmosphere.  As you get into the thicker atmosphere, then it acts as more of a conventional parachute.
Title: Re: Mars EDL technologies
Post by: alexterrell on 09/11/2009 08:12 PM
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.

Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.


Quote
Quote
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.

From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.

Yes. But the part where the thin atmosphere hurts you the most is not the initial part of the deceleration but the last part of the deceleration. Getting from 6km/s to 2km/s is no problem even with a high ballistic coefficient and the thin martian atmosphere. The part from 2km/s to subsonic is where you need the low ballistic coefficient and/or propulsive braking.

Yes, but the demand on the heat shield is much less. The heating is 1/3 or so and the force is halved. That would allow you to have a much lighter foldable heat-shield - probably all titanium and no carbon-carbon stuff. That would allow foldable heatshields.

See the picture here http://forum.nasaspaceflight.com/index.php?topic=18717.30
Title: Re: Mars EDL technologies
Post by: A_M_Swallow on 09/12/2009 03:22 AM
Are inflatable heat shields reusable?
If not a new heat shield and possible an entire lander needs bringing from Earth for each landing, this will be expensive.

Title: Re: Mars EDL technologies
Post by: Kaputnik on 09/13/2009 09:13 AM
Hey guys.

I was wondering whether anyone has thought about putting some degree of abort-to-surface capability in the mars ascent capsule?

It's quite possible that the ascent vehicle would have a large (ISRU) cryo propulsion unit and a smaller hypergol, or even monoprop, RCS/RoCS/OMS propulsion system built into the crew cabin itself. This would allow the spent cryo stage to be staged, saving overall mass. It would also provide a reliable and simple method of performing attiude/roll control, apogee burn, and rendezvous/proxops burns.
Assuming sufficient thrust from this system, it may be a relatively simply software change to allow this RCS to perform an emergency landing burn after a low-altitude cryo stage separation, i.e. in an ascent abort. This could give protection for a very early ascent abort.
Inclusion of a parachute might allow extension to later ascent aborts, but will now cost mass. To achieve aborts from later on in the ascent, a heatshield would be needed on the cabin, which adds yet more mass.

It's interesting to explore this idea, but of course the LM had no such capability and instead relied on having the upmost reliablity in the primary system.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 09/13/2009 09:37 AM
I have often heard it said that, if Apollo had been proposed today, it would have been rejected on safety grounds.

This is now the 21st century, and I think we can do better. We should do better.

- Mike
Title: Re: Mars EDL technologies
Post by: MickQ on 09/16/2009 06:54 AM
Hey guys.

I was wondering whether anyone has thought about putting some degree of abort-to-surface capability in the mars ascent capsule?

Because this is Mars, and the atmosphere is thin, I was thinking you could make the ascent capsule reallly wide and fat, but bare-boned and lightweight: Essentially extremely low-density. That way you might be able to get away with just a thin coating of PICA, and less descent propellant but huge parachutes instead. Land the thing on some giant air-bags or something. You could also use the ascent capsule as your earth-reentry capsule. That way you don't have to lug your reentry capsule all the way from earth to mars and then back again with your ERV (or MDS or transhab or whatever you want to call it).

Okay, full abort-to-surface capability might be a bit much. And you have the problem of saving the crews once they land hundreds of kilometers down-range (although this is where orbital caching of emergency supply packs can really help). So how about just a partial abort-to-surface capability: Fly a dog-leg ascent profile, and keeping the low-density capsule idea, allow an abort-to-surface during the vertical part of the ascent only. The capsule should fall nearer where they lifted off, and the sub-orbital reentry environment should be benign enough that you can keep the capsule really lightweight.

So there are two ideas here: 1) Put full EDL systems on your ascent capsule so you can use it as your earth-reentry capsule too. That way you have full abort-to-surface capability, and you don't have to lug your reentry capsule all the way from earth to mars and then back again.

And 2) Using a dog-leg ascent profile, and just putting a minimal abort-to-surface capability in the capsule to allow aborts during the vertical part of the descent only.

Both using extremely low-density capsule designs with big parachutes and minimal-mass landing systems.

Your thoughts guys?

I guess the question for (1) is: Can mars-optimized EDL systems be made to work adequately during earth-reentry (or vice-versa, whichever way you want to look at it). In other words, can you design an EDL system which can accomplish both tasks reasonably well, without resorting to complete duplication of systems?

And for (2): How lightweight can you make the capsule if you only design in abort-to-surface capability during the vertical part of ascent? And would the vertical flight phase last long enough to make a minimal abort-to-surface capability worthwhile?

- Mike

Mike.

Do your orbital supply packs include ISRU units ?? 

Mick.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 09/16/2009 08:53 AM
Mick,

I'm surprised you caught that in there ;)

As I imagine them, no. Just a couple of tonnes worth of general supplies, and maybe an inflatable shelter or something (although the capsule would be low-density to be useful for reentry, so the capsule by itself should be quite spacious).

Over at MarsDrive we're looking at an architecture which uses long-range mobile habs. In addition to the 'standard' array of safety advantages that they provide to the architecture (crew are always within stones-throw of their base, bring their radiation protection with them, no need to commute in dinky rovers, etc.) I would imagine that they could also be remotely driven. So as long as the aborted capsule lands within say a few hundred kilometers of the launch area, then it should take only a few days for the mobile habs to reach the crew for rescue. A few tonnes of supplies should last the crew a few weeks, even without recycling. So there should be ample opportunity for rescue. Our current baseline actually uses two mobile habs (as this divides their mass in half, and also allows a fully-paired approach thus further increasing mission safety). Perhaps one of them could be pre-staged downrange before the crew even attempts the ascent? Just musings at this stage of course.

You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?

Other options which might fit within the ~2 tonne payload envelope might include a small open rover with supplies, or perhaps even something like the Apollo LRF/LESS?

Interesting topic. Is there a spereate thread for 'mars rescue options' and such? I'll have a look...

- Mike
Title: Re: Mars EDL technologies
Post by: A_M_Swallow on 09/16/2009 11:15 PM

You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?

ISRU hydrogen can be made from the electrolysis of water.  Ice is suspected to be on the surface of Mars.  Ice can be melted with a lens and sunlight.
Title: Re: Mars EDL technologies
Post by: MickQ on 09/17/2009 01:31 AM
Mick,

I'm surprised you caught that in there ;)

As I imagine them, no. Just a couple of tonnes worth of general supplies, and maybe an inflatable shelter or something (although the capsule would be low-density to be useful for reentry, so the capsule by itself should be quite spacious).

Over at MarsDrive we're looking at an architecture which uses long-range mobile habs. In addition to the 'standard' array of safety advantages that they provide to the architecture (crew are always within stones-throw of their base, bring their radiation protection with them, no need to commute in dinky rovers, etc.) I would imagine that they could also be remotely driven. So as long as the aborted capsule lands within say a few hundred kilometers of the launch area, then it should take only a few days for the mobile habs to reach the crew for rescue. A few tonnes of supplies should last the crew a few weeks, even without recycling. So there should be ample opportunity for rescue. Our current baseline actually uses two mobile habs (as this divides their mass in half, and also allows a fully-paired approach thus further increasing mission safety). Perhaps one of them could be pre-staged downrange before the crew even attempts the ascent? Just musings at this stage of course.

You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?

Other options which might fit within the ~2 tonne payload envelope might include a small open rover with supplies, or perhaps even something like the Apollo LRF/LESS?

Interesting topic. Is there a spereate thread for 'mars rescue options' and such? I'll have a look...

- Mike

Hey Mike.

I was thinking along the lines of if the capsule came down somewhere not easily accessable for a rescue, say down in Marineris or on  Olympus as  extreme examples, then it could be quite a while before they hook up with a Hab/rover.  Water and oxygen may run short especially if one or more of the crew are injured or are actively trying to find a way out.

Mick
Title: Re: Mars EDL technologies
Post by: MickQ on 09/17/2009 01:42 AM
Mick,

I'm surprised you caught that in there ;)

As I imagine them, no. Just a couple of tonnes worth of general supplies, and maybe an inflatable shelter or something (although the capsule would be low-density to be useful for reentry, so the capsule by itself should be quite spacious).

Over at MarsDrive we're looking at an architecture which uses long-range mobile habs. In addition to the 'standard' array of safety advantages that they provide to the architecture (crew are always within stones-throw of their base, bring their radiation protection with them, no need to commute in dinky rovers, etc.) I would imagine that they could also be remotely driven. So as long as the aborted capsule lands within say a few hundred kilometers of the launch area, then it should take only a few days for the mobile habs to reach the crew for rescue. A few tonnes of supplies should last the crew a few weeks, even without recycling. So there should be ample opportunity for rescue. Our current baseline actually uses two mobile habs (as this divides their mass in half, and also allows a fully-paired approach thus further increasing mission safety). Perhaps one of them could be pre-staged downrange before the crew even attempts the ascent? Just musings at this stage of course.

You've actually brought up quite an interesting question. Perhaps the case can be made for a small ISRU plant and recyling onboard the orbitally cached 'rescue pack'? But keeping in mind that this thing would be in orbit for at least a few years before being used and therefore cant really store hydrogen onboard, then what sort of ISRU could you use?

Other options which might fit within the ~2 tonne payload envelope might include a small open rover with supplies, or perhaps even something like the Apollo LRF/LESS?

Interesting topic. Is there a spereate thread for 'mars rescue options' and such? I'll have a look...

- Mike

Hey Mike.

I was thinking along the lines of if the capsule came down somewhere not easily accessable for a rescue, say down in Marineris or on  Olympus as  extreme examples, then it could be quite a while before they hook up with a Hab/rover.  Water and oxygen may run short especially if one or more of the crew are injured or are actively trying to find a way out.

Mick

Another thought.  Maybe for your rescue pack or just as a general piece of exploration equipment,  remember the old "Lost in Space" rocket pack.  How would something like that work in Mars G with methane fuel?

Mick.
Title: Re: Mars EDL technologies
Post by: jongoff on 10/17/2009 12:48 AM
Fun article in the latest AIAA Journal of Spacecraft and Rockets (Vol. 46, No. 5, September–October 2009):

"Survey of Supersonic Retropropulsion Technology for Mars Entry, Descent, and Landing" by Ashley M. Korzun, Robert D. Braun of Georgia Institute of Technology, and Juan R Cruz of NASA Langley.

It was a pretty interesting review of all the work done over the past 50 years on the topic.  Apparently it looks like having a few peripheral rocket engines ends up being much more effective than a central rocket engine.  Still more work to be done, but I figured I'd share the reference.

~Jon
Title: Re: Mars EDL technologies
Post by: MickQ on 11/06/2009 01:02 AM
Has anyone done any work on parachute/parafoil landing systems recently for Mars ???   Is there a formula for area vs landing mass ???

Mick.
Title: Re: Mars EDL technologies
Post by: Jim on 11/06/2009 01:11 AM
Has anyone done any work on parachute/parafoil landing systems recently for Mars ???   Is there a formula for area vs landing mass ???


Parachutes can't be use for landing, only deceleration.  Rockets or airbags are needed for final descent
Title: Re: Mars EDL technologies
Post by: MickQ on 11/06/2009 01:24 AM
Has anyone done any work on parachute/parafoil landing systems recently for Mars ???   Is there a formula for area vs landing mass ???


Parachutes can't be use for landing, only deceleration.  Rockets or airbags are needed for final descent

Sorry Jim.  I should have said Descent Mass.  I was just trying to relate chute size to what you might try to put on the surface.

Mick.
Title: Re: Mars EDL technologies
Post by: MickQ on 11/12/2009 02:02 AM
Some time ago I read something about the shape of a "Shuttlecock" being investigated for use in aero-braking.

Anyone heard this ???

Mick.
Title: Re: Mars EDL technologies
Post by: jml on 11/12/2009 03:01 AM
Some time ago I read something about the shape of a "Shuttlecock" being investigated for use in aero-braking.

Anyone heard this ???

Mick.
You mean like Burt Rutan's SS1?
Title: Re: Mars EDL technologies
Post by: Danny Dot on 11/12/2009 03:07 AM
I would be glad to help out on these thread if we can stick to english.  I literally can't read most of the posts here. 

Danny Deger
Title: Re: Mars EDL technologies
Post by: MickQ on 11/12/2009 04:56 AM
Some time ago I read something about the shape of a "Shuttlecock" being investigated for use in aero-braking.

Anyone heard this ???

Mick.
You mean like Burt Rutan's SS1?

Not as such, though I think the basic principle applies to Space Ship One.

What I was refering to is something like a stiff skirt fixed to the rear of an  entry vehicle that acts in the same way as a shuttlecock to slow and stabilize the craft for a substantial part of it's descent before parachutes and/or propulsive systems take over. 

Mick.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/20/2010 09:24 AM
Question:

Could a viking-style entry vehicle, designed for the martian entry environment, theoretically also work sufficiently well at earth-entry?

I'm thinking it might; as presumably you can just open the chutes at an earth altitude analogous to that which they are designed for deploying at mars, right?

In other words, whatever the entry environment they are designed for at mars (the determining factors being entry speed and atmospheric pressure) can presumably be found at some entry altitude at earth: Just pop the chutes at that altitude, and the lander should glide safely down to earth, right?

Or not? The major spanner in the works that I can see is the possibility that the entry vehicle will enter the thicker part of the earths atmosphere too fast, as the deceleration is far less at the higher mars-analog altitude. Therefore, the parachutes may be under far more stress at this point. In other words, the maximum dynamic pressure may be much higher during earth entry than at mars entry.

However, current parachute technology seems to handle such pressures reasonably well (e.g. Apollo, StarDust, etc.). So I can only assume that, if the "max q" at earth entry is much greater than at mars entry, that this would not be a major problem to deal with (if one was inclined to design a parachute system that worked equally well for both entry environments, for whatever reason that may be ;-).

The reason I ask, of course, is that I want to look into the possibility, for a manned-mars-mission, of re-using the mars ascent capsule as the crews earth-reentry capsule. Doing that may be a good trade for a few reasons (as surmised during previous posts in this thread):

1. It means the ERV staged in mars' orbit doesn't have to carry a dedicated earth-reentry capsule all the way from earth to mars' orbit and then back again. You could add a little more mass to the ERV vehicle instead.

2. The ascent capsule and earth reentry capsule both have similar requirements, functions, and restraints: They both need to be as lightweight as possible, yet have just enough volume to accomodate the full mission crew for a few days at most. They also both need comms equipment, an OMS, life support, a few days worth of supplies, etc.

3. Putting mars-qualified re-entry systems on the capsule would allow an abort-to-surface anywhere within the ascent profile. That is perhaps only beneficial if your particular architecture is able to support the crews wherever they happen to land during an abort. As per previous posts, a maximally dog-leg ascent profile is envisioned, but it is also conceivable that we could land the next missions assets beside the crew wherever they happen to land their capsule, or else send a dedicated 'emergency supply' vehicle that had been previously staged in mars' orbit for just a contingency.

4. Why not? I don't see any huge disadvantages. Except perhaps that the ascent capsule will be heavier (given that it now has a heatshield and parachutes to be able to abort-to-surface; I envision that the small retro-rocket stage required for mars-landing would be used to provide the final boost to orbit or else be integrated with the OMS system anyway). But in our particular case, this may not be so much of an issue, as we have plenty of spare margin available in our ascent fuel-producing ISRU lander.

Any takers please?

Thanks in advance.

- Mike
Title: Re: Mars EDL technologies
Post by: Hop_David on 01/20/2010 02:40 PM
Is there a formula for area vs landing mass ???

Mick.

I think you're thinking of the ballistic coefficient (http://en.wikipedia.org/wiki/Ballistic_coefficient).

If you examine the formula in the Wikipedia article I linked to, you'll see mass and cross sectional area are in the formula.

Also in the equation is density. A thin atmosphere makes it harder to slow stuff down.

In my opinion, one of the more interesting efforts to increase cross sectional area are inflatable heat shields.

As stuff gets bigger, it gets harder to slow down. All these objects have the same ratio of mass to cross sectional area:
(http://clowder.net/hop/BallisticCoeff.jpg)

Which is why it's easier to land a rover than a hab:
(http://clowder.net/hop/TMI/ZubrinFairy.jpg)
Title: Re: Mars EDL technologies
Post by: Kaputnik on 01/21/2010 11:08 AM
Fun article in the latest AIAA Journal of Spacecraft and Rockets (Vol. 46, No. 5, September–October 2009):

"Survey of Supersonic Retropropulsion Technology for Mars Entry, Descent, and Landing" by Ashley M. Korzun, Robert D. Braun of Georgia Institute of Technology, and Juan R Cruz of NASA Langley.

It was a pretty interesting review of all the work done over the past 50 years on the topic.  Apparently it looks like having a few peripheral rocket engines ends up being much more effective than a central rocket engine.  Still more work to be done, but I figured I'd share the reference.

~Jon

Thanks, Jon. Hypersonic retropropulsion could be a complete game-changer for Mars EDLS. Although it could also be a case of 'throwing mass at the problem'.

If we can land things in bigger chunks, it challenges a lot of the other assumptions about the mission, e.g. ISRU, the degree of mobility required, loiter time for previously landed cargoes etc.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/21/2010 12:46 PM
That cartoon is great. It also illustrates why with an HLV you will always be struggling with mass constraints if you want to launch everything in one go whereas existing EELVs are more than enough for launching dry-launched pieces.
Title: Re: Mars EDL technologies
Post by: Lampyridae on 01/25/2010 02:05 AM
Question:

Could a viking-style entry vehicle, designed for the martian entry environment, theoretically also work sufficiently well at earth-entry?

I'm thinking it might; as presumably you can just open the chutes at an earth altitude analogous to that which they are designed for deploying at mars, right?


Nope. Different gases behave differently, requiring different heatshield designs. The Sovs lost their Mars probes because they thought Mars had an N2 atmosphere. It didn't, as we know, and the first pictures of the Martian surface came from the Vikings.

On the other hand, a spherical heatshield will work for both cases. But for Mars it must be very, very fluffy indeed. It is also very hard to steer.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/25/2010 06:54 AM
Question:

Could a viking-style entry vehicle, designed for the martian entry environment, theoretically also work sufficiently well at earth-entry?

I'm thinking it might; as presumably you can just open the chutes at an earth altitude analogous to that which they are designed for deploying at mars, right?


Nope. Different gases behave differently, requiring different heatshield designs. The Sovs lost their Mars probes because they thought Mars had an N2 atmosphere. It didn't, as we know, and the first pictures of the Martian surface came from the Vikings.

On the other hand, a spherical heatshield will work for both cases. But for Mars it must be very, very fluffy indeed. It is also very hard to steer.

I would have preferred a longer answer, but I'll take your word for it. On to the next question then: What sort of engineering compromises would you have to make to have a capsule work sufficiently well at both entry environments?

It would seem to me as though the shape of the entry vehicles itself is quite suited to both (as we have used the same basic shape in both environments many times before). Perhaps it is just the heatshield? Both mars-entry and earth-entry designs have used PICA. Perhaps you just need a slightly thicker one for earth-entry, to sustain the higher peak heat flux(?), or can the internal composition of such heatshields also change?

Lets also assume that your mass to cross-sectional area ratio is the same as the Viking designs also (i.e. density). Could the mars-optimized chutes be used sufficiently well at earth-entry? Or would you need to compromise them somewhat to be any good at both entry environments?

- Mike
Title: Re: Mars EDL technologies
Post by: Jim on 01/25/2010 08:52 AM

Lets also assume that your mass to cross-sectional area ratio is the same as the Viking designs also (i.e. density). Could the mars-optimized chutes be used sufficiently well at earth-entry? Or would you need to compromise them somewhat to be any good at both entry environments?


No. Mars chutes are not used to land the vehicle.  Mars chutes were/are tested at 100k feet to get the equivalent conditions on earth.

Mars chutes are designed for total different conditions.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/26/2010 04:29 AM

Lets also assume that your mass to cross-sectional area ratio is the same as the Viking designs also (i.e. density). Could the mars-optimized chutes be used sufficiently well at earth-entry? Or would you need to compromise them somewhat to be any good at both entry environments?


No. Mars chutes are not used to land the vehicle.  Mars chutes were/are tested at 100k feet to get the equivalent conditions on earth.

Mars chutes are designed for total different conditions.

Yes, I understand that. But how useful might a mars-optimized chute be for earth entry? Instead of discarding it early to allow a rocket-assisted landing, as on mars, how useful would the same design be if, during earth-entry, you were to keep it for longer? Would there be any additional forces during earth-entry that are not present during mars-entry that could break it later in the descent? And, if not, would the mars-optimized chute provide a reasonable terminal velocity that you could... Okay scratch that question..

The real question I am interested in is this:

What sort of engineering compromises would you have to make to a manned mars ascent capsule, assuming it already has abort-to-surface (mars' surface, not earths) capability, work reasonably well at earth-entry?

Lets assume a large Viking-heritage capsule shape, perhaps 5m in diameter, and with mach 2.5 or thereabout chutes and an appropriate amount of fuel and thrust for the purely propulsive phase of descent required to comfortably land on mars'surface.

Or, alternatively, if you want a question that sounds silly but is perhaps easier to analyze: What sort of additions would you need to make to a Viking lander, if back in 1975, the anti-nuclear 'hippies' hassled NASA enough that they had to design abort-to-surface capability into the lander, just in case the upper stage malfunctioned and the craft was bound to eventually crash back to earth (perhaps from a highly elliptic orbit), thus preventing distribution of radiocative particles into the atmosphere from their giant (again, theoretical) RTG?

I wish I didn't have to say it that way, but perhaps you'll now understand my question better.

Thanks,

- Mike
Title: Re: Mars EDL technologies
Post by: neilh on 04/23/2010 11:44 PM
There's probably something I'm missing that makes this idea completely silly, but what about increasing air resistance with some sort of mesh or net? For example, if you wanted to aerobrake a Bigelow station into Mars orbit you could stretch some sort of high-drag mesh between the multiple modules to help it slow down.

In the extreme case, I guess you could imagine something like a Borg cube, with a highly open design and plenty of bits on the inside to maximize drag. ;)
Title: Re: Mars EDL technologies
Post by: Robotbeat on 04/24/2010 11:00 PM
There's probably something I'm missing that makes this idea completely silly, but what about increasing air resistance with some sort of mesh or net? For example, if you wanted to aerobrake a Bigelow station into Mars orbit you could stretch some sort of high-drag mesh between the multiple modules to help it slow down.

In the extreme case, I guess you could imagine something like a Borg cube, with a highly open design and plenty of bits on the inside to maximize drag. ;)

I don't think that much matters besides the frontal area and maybe angle-of-attack when the mean-free path of the air molecules is of the same order-of-magnitude or greater as the spacecraft. Otherwise, a parachute is pretty well optimized to increase the drag coefficient, at least for subsonic velocities (don't know about supersonic).

This post is based mostly on the physical intuition of someone with a BS* in Physics, so take it for what it's worth, and maybe a pinch of salt. ;)

*(heh, incorrect filter strikes again! I take offense at that! ;) )
Title: Re: Mars EDL technologies
Post by: Robotbeat on 04/24/2010 11:23 PM
Here's an interesting paper:
"A Survey of Supersonic Retropropulsion Technology for Mars Entry, Descent, and Landing" December 2007 or so. Worth reading!
Title: Re: Mars EDL technologies
Post by: Robotbeat on 04/24/2010 11:35 PM
Basically, the most insightful thing I gained from that paper is:
For low-thrust supersonic retropropulsion, if you put your nozzle in the center of the capsule, it actually decreases total deceleration compared to not firing it at all because of how it interacts with the shock layer, but if you have multiple nozzles arranged on the periphery as pictured, total deceleration (aerodynamic plus thrust) is greater than just the aerodynamic deceleration.
Title: Re: Mars EDL technologies
Post by: TrueBlueWitt on 04/25/2010 12:56 AM
Could you use something like laminar exterior flow rockets to do the opposite.. create an exterior cone that would funnel more Mars atmosphere at the  heat shield?

           
         __
       o/  \o
      //    \\
     / ====== \
    /          \
   /            \


A bit like MLAS, but a complete cone at high velocity but very thin with low mass flow rates.. a curtain of sorts
Title: Re: Mars EDL technologies
Post by: mike robel on 04/25/2010 01:12 AM
This is interesting.  On the Training Sabot round for the 120mm gun, the penetrator is stabalized by a cone that is perforated in the way you describe. Out to about 1500 meters, the velocity and ballistics match the service round, but after that, the perforations rapidly decellerate the round, causeing it to need no more room than the old 105mm spit stabalized training round.  Very important for places that do not have mountains to stop the shot...
Title: Re: Mars EDL technologies
Post by: MickQ on 04/29/2010 04:14 AM
There's probably something I'm missing that makes this idea completely silly, but what about increasing air resistance with some sort of mesh or net? For example, if you wanted to aerobrake a Bigelow station into Mars orbit you could stretch some sort of high-drag mesh between the multiple modules to help it slow down.

In the extreme case, I guess you could imagine something like a Borg cube, with a highly open design and plenty of bits on the inside to maximize drag. ;)

You may be interested in taking a look at the " Landing Heavy Loads On Mars " thread.

From the discussion there,  I don't think anything short of a full coverage heatshield or parachute braking system is going to have any usefull effect.

Mick.
Title: Re: Mars EDL technologies
Post by: Nathan on 05/22/2010 11:20 PM
I don't understand why deployable heat shields are no longer discussed for mars edl. They were a feature of many mars mission architectures including Mars Direct. Was there a showstopper? Some links below.

http://www.freepatentsonline.com/20080078884.pdf

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=2003ESASP.521..247T&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES
Title: Re: Mars EDL technologies
Post by: Archibald on 01/13/2011 02:28 PM
This article gives a summary of Mars Exploration Entry, Descent and Landing Challenges (http://www.4frontierscorp.com/dev/assets/Braun_Paper_on_Mars_EDL.pdf).

Bringing this back to life...

The article clearly states that
Quote

To date, no credible Mars EDL architecture has
been put forward that can safely place a 2 t payload at high
elevations on the surface of Mars at close proximity to
scientifically interesting terrain.


Warning: hare brained idea. Got bored at work :)

Ok, so as of today we can't land more than 2 tons. Right. Now let's suppose that we reach Phobos one day.

The problem remains that we still can't land more than 2 tons to Mars surface.
The only manned ship I can' think of that weighed less than 2 tons was the Mercury capsule. 1360 kg as far as I remember. That was 50 years ago however; a moder-day variant would certainly weight 800 kg, perhaps even less.

So the question is: could a modern day Mercury, with a mass increased near *Braun 2 tons limit*, land a single man on Mars after departing from Phobos ?

To ease things and cut mass, we suppose this would be a one way trip - for the descent ship, but not for the astronaut !
For return we suppose that our astronaut transfer to a similar vehicle, send previously to the surface (pin point landing, akin to Apollo 12 and Surveyor)

Of course that a lot of risk, for very little return. The poor guy would spent only hours, if not minutes, on the surface...
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/13/2011 09:14 PM
If you double the heatshield area and parachute area you should get about double the payload to the surface. 2 tonnes is only a real constraint if the launch vehicles payload fairing is restricted to 5m. The same EDL system as used on MSL could conceivably be scaled-up if given enough PLF volume. Parachutes don't tend to scale as well as everything else, but perhaps it might be possible to cluster them, or stage them (single supersonic 'chute quickly followed by a cluster of subsonic 'chutes).

With a 9m diameter entry vehicle (4 times the area of MSL's 4.5m diameter) up to 7 tonnes surface payload may be possible; with the help of a triple-cluster of MSL-sized 'chutes (like Apollo or Dragon), more efficient bipropellant descent stage (MSL uses inefficiet monopropellant), reduced hover time, and lower landing altitude.

7 tonnes may not be enough for a full 4-person Hab with onboard consumables.

But it could be enough for a large 2-person rover with limited consumables.

Landing two of these in parallel would ensure that the full crew of 4 are able to access consumables and other assets which are landed ahead of their arrival.

See the link in my sig for more thoughts on this.

- Mike
Title: Re: Mars EDL technologies
Post by: MickQ on 01/25/2011 06:27 AM
A few questions for those more in the know than I.

1.   Is it any easier, safer or more precise to land from orbit than from a ballistic direct entry ?

2.   If a craft were to brake heavily while in orbit and then follow a more vertical descent profile, would the slower entry velocity therefore allow heavier or larger payloads to be landed or allow payloads to be landed at higher altitudes ?

Mick.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/25/2011 08:42 AM
2.   If a craft were to brake heavily while in orbit and then follow a more vertical descent profile, would the slower entry velocity therefore allow heavier or larger payloads to be landed or allow payloads to be landed at higher altitudes ?

Yes, but it would take a lot more propellant. Not necessarily prohibitively so, comparable to combined moon ascent and descent, only you need to preposition that propellant in LMO instead of LLO. This could be interesting if you used SEP to preposition the propellant and had cheap lift and wanted to avoid the need for an HLV. Even so you would want to use aerodynamic deceleration to the maximum extent possible.
Title: Re: Mars EDL technologies
Post by: Hop_David on 01/25/2011 08:54 AM
If you double the heatshield area and parachute area you should get about double the payload to the surface.

Surface to volume ratio decreases as size increases. So mass won't scale linearly to surface of heatshield.

These all have same ballistic coefficient:
(http://clowder.net/hop/BallisticCoeff.jpg)
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/25/2011 02:50 PM
If you double the heatshield area and parachute area you should get about double the payload to the surface.

Surface to volume ratio decreases as size increases. So mass won't scale linearly to surface of heatshield.

These all have same ballistic coefficient:
(http://clowder.net/hop/BallisticCoeff.jpg)
Of course, that's what he said! He said that if you double the heatshield and parachute area, you get double the payload (for the same ballistic coefficient). Which is true.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/25/2011 06:16 PM
Thanks Chris. It might also be worth noting that a crewed rover, with limited consumables, is quite a low-density payload. Unlike robotic landers, a crewed lander would be mostly empty space. That means your entry vehicle doesn't have to look like an inverted chinese hat to get the necessary low ballistic coefficient.
Title: Re: Mars EDL technologies
Post by: tnphysics on 01/25/2011 08:44 PM
What about a winged vehicle? Or CO2-breathing descent propulsion?

I was thinking a propeller (like a chopper).
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/25/2011 08:54 PM
What about a winged vehicle? Or CO2-breathing descent propulsion?

I was thinking a propeller (like a chopper).
The atmosphere has less than 1% the pressure of Earth. You're practically in a vacuum.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/25/2011 09:06 PM
Amazingly there have been proposals for Mars helicopters for small payloads. It may be barely feasible, but it looks very impractical.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/25/2011 09:16 PM
Amazingly there have been proposals for Mars helicopters for small payloads. It may be barely feasible, but it looks very impractical.
Right, it may be possible, but not practical (for large payloads).
Title: Re: Mars EDL technologies
Post by: tnphysics on 01/26/2011 10:43 PM
What about a winged vehicle?
Title: Re: Mars EDL technologies
Post by: Archibald on 01/27/2011 07:15 AM
Amazingly there have been proposals for Mars helicopters for small payloads. It may be barely feasible, but it looks very impractical.

 "helicopters don't fly, they beat CO2 at 1% of the pressure of Earth  into submission"
Title: Re: Mars EDL technologies
Post by: MarsInMyLifetime on 01/27/2011 02:31 PM
What about a winged vehicle?

Were you aware of this proposed mission? To my knowledge, it is still on the shelf, but very much a contender, if future science budgets permit.
http://marsairplane.larc.nasa.gov/index.html (the other ARES)

The winged concept is feasible, but only at a fairly high cruising speed. This craft uses rocket propulsion to keep up the lift for its 2-hour mission.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/27/2011 04:16 PM
What about a winged vehicle?

Were you aware of this proposed mission? To my knowledge, it is still on the shelf, but very much a contender, if future science budgets permit.
http://marsairplane.larc.nasa.gov/index.html (the other ARES)

The winged concept is feasible, but only at a fairly high cruising speed. This craft uses rocket propulsion to keep up the lift for its 2-hour mission.

It's not a completely impossible idea that you could have a propeller-driven winged vehicle flying around the lower altitude areas of Mars. The highest flight of a propeller-driven winged vehicle I believe was to about 67,000 ft (by a Boeing UAV). The pressure there is about 5% of atmospheric pressure, but Mars gravity is a little more than one third Earth gravity, so from a lift/weight standpoint, it might be possible someday.

(You want to use a propeller instead of a turbine because a propeller moves slower through the air than turbine blades of the same thrust... Slower means less power required for the same thrust.)

You'd probably want to figure out some sort of chemical reaction that uses carbon dioxide... or perhaps some sort of air-augmented rocket would work to give you a higher effective ISP than just a straight rocket.

But it doesn't make a heck of a lot of sense for an EDL technology.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/27/2011 04:53 PM
Why wouldn't a lifting entry make sense for EDL?
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/27/2011 05:10 PM
Why wouldn't a lifting entry make sense for EDL?
I didn't say a lifting entry makes no sense (after all, even current capsules have a little lift during reentry), I said that using wings for Entry, Descent, and Landing doesn't make much sense. It'd essentially be like trying to land at 100,000 feet.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/27/2011 05:16 PM
OK, what would be the downside of using wings specifically? I thought they might be more useful in the rarified Martian atmosphere than a lifting body, but maybe they aren't.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/27/2011 05:25 PM
OK, what would be the downside of using wings specifically? I thought they might be more useful in the rarified Martian atmosphere than a lifting body, but maybe they aren't.
You'd be trying to land practically in a vacuum. I don't know that a lifting body would be terribly useful, either. If you're traveling at subsonic velocities (which is necessary for any kind of safe landing), you wouldn't be generating enough lift to avoid stalling unless you had just ENORMOUS wings. You may not be able to build wings light enough for such a task.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/27/2011 05:35 PM
Oh absolutely, but I was thinking of using them to buy you time to decelerate aerodynamically before you run out of altitude and to give you cross-range. Wings are useless for takeoff and landing itself. That was one of the things Orbiter taught me early on. I had no idea the Martian atmosphere is as thin as it is.
Title: Re: Mars EDL technologies
Post by: MarsInMyLifetime on 01/27/2011 06:23 PM
Rob Manning, who managed the Pathfinder and MER EDL programs for NASA, has a number of writings about the unique difficulties of Mars EDL. Here are links to an informal discussion and a more academic look at the limits of various current technologies.

http://www.universetoday.com/7024/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
http://journalofcosmology.com/Mars146.html

I see that there are papers about "deployable decelerators." The principle is still that of creating the highest possible drag with a direct entry, then transitioning to a propulsive lander, and using "lift" during the entry phase to refine your landing as closely as possible. Eliminating the parachute phase would certainly help cut down the complexity of the EDL sequence, but for now, Rob indicates that a parachute is pretty much required to get into the subsonic regime for the retros or other landing system to start their work.

The ill-fated Beagle lander relied on a parachute to the surface with airbags to brake the impact. We may never know why it failed, but it was clearly right on the margin of being successful at all, and it was on the small end of things.
Title: Re: Mars EDL technologies
Post by: Aeroman on 01/27/2011 06:40 PM

The ill-fated Beagle lander relied on a parachute to the surface with airbags to brake the impact. We may never know why it failed, but it was clearly right on the margin of being successful at all, and it was on the small end of things.

But they did find out how the Beagle Lander failed.  Didn't you see the first Transformers movie?  :-D
Title: Re: Mars EDL technologies
Post by: tnphysics on 01/27/2011 07:39 PM
What about balloons, filled with He and made of a heat-resistant material, for an ultra-compact (can be inflated and deflated easily) and ultra-fluffy (once deployed) reentry and landing system?

The balloon would deploy in vacuum. It would provide braking, initially by drag and later by buoyancy. The vehicle would land with it (the same way as balloons on earth) and then stow it. It could be re-inflated for flight within the atmosphere. The entire apparatus would be fully reusable, needing only refueling for launch back to LMO, and would use a nuclear reactor driving a propeller for atmospheric flight.

Alternately, the balloon could deploy later, with a regular heat shield. This might be needed if the balloon would collapse under reentry stresses.
Title: Re: Mars EDL technologies
Post by: Nathan on 01/27/2011 08:11 PM
Can anyone point me to a paper detailing All-propulsive edl on mars? I have read i once but cannot locate it. It was interesting because it still used air drag to help slow the vehicle down and this provided a fuel saving.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/27/2011 08:20 PM
What about balloons, filled with He and made of a heat-resistant material, for an ultra-compact (can be inflated and deflated easily) and ultra-fluffy (once deployed) reentry and landing system?

The balloon would deploy in vacuum. It would provide braking, initially by drag and later by buoyancy. The vehicle would land with it (the same way as balloons on earth) and then stow it. It could be re-inflated for flight within the atmosphere. The entire apparatus would be fully reusable, needing only refueling for launch back to LMO, and would use a nuclear reactor driving a propeller for atmospheric flight.

Alternately, the balloon could deploy later, with a regular heat shield. This might be needed if the balloon would collapse under reentry stresses.
You're describing a ballute, though deflating then reinflating it with the same gas (i.e. recycle the gas) wouldn't be possible without far too much equipment, nor would it even possibly be able to be light enough to be buoyant while also surviving reentry.
Title: Re: Mars EDL technologies
Post by: Lampyridae on 01/29/2011 06:57 AM
What about balloons, filled with He and made of a heat-resistant material, for an ultra-compact (can be inflated and deflated easily) and ultra-fluffy (once deployed) reentry and landing system?

The balloon would deploy in vacuum. It would provide braking, initially by drag and later by buoyancy. The vehicle would land with it (the same way as balloons on earth) and then stow it. It could be re-inflated for flight within the atmosphere. The entire apparatus would be fully reusable, needing only refueling for launch back to LMO, and would use a nuclear reactor driving a propeller for atmospheric flight.

Alternately, the balloon could deploy later, with a regular heat shield. This might be needed if the balloon would collapse under reentry stresses.
You're describing a ballute, though deflating then reinflating it with the same gas (i.e. recycle the gas) wouldn't be possible without far too much equipment, nor would it even possibly be able to be light enough to be buoyant while also surviving reentry.

I wouldn't trust such a thing to hold up to multiple re-entries AND re-deployment, especially into a dusty, cold, charged environment.
Title: Re: Mars EDL technologies
Post by: guru on 01/29/2011 02:45 PM
Can anyone point me to a paper detailing All-propulsive edl on mars? I have read i once but cannot locate it. It was interesting because it still used air drag to help slow the vehicle down and this provided a fuel saving.

This is the first one I thought of:

http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf

(Didn't show up on a google search, though, so I had to mine Braun's publication list, which is quite expansive and has some very interesting papers:

http://soliton.ae.gatech.edu/people/rbraun/publications.pdf )
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 09:38 PM
Heh, payload mass fractions of only 2.5%(!) for fully-propulsive descent - and that is from orbit! Doesn't look very promising to me...
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/29/2011 09:47 PM
The study doesn't take the possibility of transporting the propellant by SEP into account.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 10:27 PM
How would that help?
Title: Re: Mars EDL technologies
Post by: guru on 01/29/2011 10:40 PM
Heh, payload mass fractions of only 2.5%(!) for fully-propulsive descent - and that is from orbit! Doesn't look very promising to me...

I'm not defending this as the best way forward, but take it all in context - that's the low end.  The upper limit of what was presented in this study is 8.7% for an appromixate 100 mT initial mass.  That might not compare well to the 25-35% we get now, but it does mean that you could land about 8.4 mT without the requiring any of the following:

"aeroassist technology elements such as lifting aeroshell configurations, an ablative thermal protection system, parachutes, or inflatable aerodynamic decelerators (IAD)."

8.4 mT is enough to land all elements of the Mobile Hab architecture that you are working at MarsDrive with an additional 20% mass margin.

Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 10:56 PM
Yes but 100mT entry mass does not compare too favorably with 17mT entry mass for the same surface payload. ;-)

It is interesting to me that, as far as I can tell, not a single study has been done to address the question of "how far can heritage EDL tech be pushed?".

All seem to assume that some form or other of exotic tech is required for anything more than about 2mT... But I don't think that that is the case.

Without the restriction of Atlas V's 5m PLF, the heatshield could conceivably be scaled up from 4.5m to 9m diameter - still allowing it to be launched in one-piece via SLS or the like. If the parachutes are also scaled up (perhaps by clustering 3 smaller ones together), then that should allow over 4mT payload.

A low landing altitude, more efficient bipropellant descent stage, reduced hover time, higher L/D ratio, etc. are used then perhaps this could conceivably be pushed up to 7mT.

The question then becomes, what can we do with 7mT at a time? Of course, I think I have that one answered. ;-)
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/29/2011 11:01 PM
How would that help?

You may need more propellant, but you can transport it more efficiently than with chemical propulsion - unlike a heatshield.
Title: Re: Mars EDL technologies
Post by: guru on 01/29/2011 11:01 PM
How would that help?

Electric propulsion wouldn't help at all getting you from Mars orbit to the surface, but it would be a major help in getting the propellant from Earth orbit to Mars orbit.

For example, say I need to send 100 tonnes to Mars orbit starting from Earth orbit.  If all I have is chemical propulsion with 450 s Isp, then I need about 300 tonnes in LEO to get through TMI, just to land one of four mission elements.

If, on the other hand, I have a 100 kW VASIMR with 5000 s Isp, then I only need about 130 mT (14 tonnes propellant, 14 tonnes solar panels, 2 tonnes engine).   This provides 5.4 km/s delta V which is enough to carry it from LEO to Mars Orbit.  Now, I just need a Falcon-X heavy for each element, but that's better than three of them per element.

(Obviously, flying through the Van Allen belts is not good for the crew, but one of the supposed advantages of VASIMR is that the engine could theoretically produce a magnetic field for radiation protection - discussion for another thread.)
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 11:10 PM
A 125mT to LEO Falcon X Heavy is required to achieve just 8.4mT surface payload? That is still a pretty inefficient system. With conventional EDL tech, you could almost get twice that.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/29/2011 11:21 PM
A 125mT to LEO Falcon X Heavy is required to achieve just 8.4mT surface payload? That is still a pretty inefficient system. With conventional EDL tech, you could almost get twice that.

My interest in highly propulsive EDL (not fully propulsive, no need to avoid low hanging fruit) is to provide for as large a propellant market as possible without undue cost. In other words, to maximise propellant mass in LEO under the constraint that total mission cost remains constant.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 11:42 PM
A 125mT to LEO Falcon X Heavy is required to achieve just 8.4mT surface payload? That is still a pretty inefficient system. With conventional EDL tech, you could almost get twice that.

My interest in highly propulsive EDL (not fully propulsive, no need to avoid low hanging fruit) is to provide for as large a propellant market as possible without undue cost. In other words, to maximise propellant mass in LEO under the constraint that total mission cost remains constant.

That's backwards. The economics will never support it.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/29/2011 11:48 PM
That's backwards. The economics will never support it.

No, it's not backwards, by definition even, because of the constraint of keeping cost constant, which will be a strong constraint initially. But the point is to achieve economies of scale through commercial development of cheap lift. That requires a market, which is what highly propulsive solutions can provide. RLVs could reduce launch prices by an order of magnitude.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/29/2011 11:56 PM
But you don't "create a market" with the purpose of reducing the cost of supplying itself. That doesn't make any sense.

The cost must be reduced first. Otherwise there is no economic incentive for the market to exist in the first place.

The only way you can get around this fundamental rule of economics is with government procurement. But even then, it is still bad economics.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/30/2011 12:11 AM
The only way you can get around this fundamental rule of economics is with government procurement.

Yes, and that's what we're talking about here. Money that will be spent on exploration - hypothetically anyway - that can do double duty as extra demand for commercial launch vehicles.

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But even then, it is still bad economics.

No, it means more bang for your buck, that's more economical.

Are we really talking about the same thing here? I'm talking about looking at all technical solutions that fit a fixed cost profile and then choosing the one that use the most propellant to maximise the synergy with development of cheap lift. Initially that might be only a bit more propulsive than traditional solutions (except for very heavy payloads), but as launch prices came down you could go more and more propulsive.

You could also try to spend as much as possible on spacecraft if you want to stimulate commercial spacecraft R&D, advanced high Isp propulsion if that's your thing and so on. Which of these you would choose would depend on what your goals are.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/30/2011 12:34 AM
For a given amount of surface payload, you are asking for twice as much IMLEO. For this reason, I don't think such an inefficient propulsive descent will be anywhere inside your fixed cost profile to begin with. If it were, you must be expecting that launch prices are halved when launch demand is doubled. Which would be a very bad assumption.
Title: Re: Mars EDL technologies
Post by: Nathan on 01/30/2011 12:57 AM
Can anyone point me to a paper detailing All-propulsive edl on mars? I have read i once but cannot locate it. It was interesting because it still used air drag to help slow the vehicle down and this provided a fuel saving.

This is the first one I thought of:

http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf

(Didn't show up on a google search, though, so I had to mine Braun's publication list, which is quite expansive and has some very interesting papers:

http://soliton.ae.gatech.edu/people/rbraun/publications.pdf )

Ah that's the one -thanks. I couldn't remember the conclusion but it seems it's only viable with isp of 650s or more.
Title: Re: Mars EDL technologies
Post by: Nathan on 01/30/2011 01:01 AM
A 125mT to LEO Falcon X Heavy is required to achieve just 8.4mT surface payload? That is still a pretty inefficient system. With conventional EDL tech, you could almost get twice that.

It's the simplicity that is the benefit - no need to develop heavy heatshileds, supersonic parachutes etc.
Thrusting into a hypersonic flow is the problem here though.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 01/30/2011 01:18 AM
But heavy heatshields and supersonic parachutes have already been developed. They will fly on MSL later this year.
Title: Re: Mars EDL technologies
Post by: kkattula on 01/30/2011 01:32 AM
How would that help?

You may need more propellant, but you can transport it more efficiently than with chemical propulsion - unlike a heatshield.

What says you can't send a heatshield via SEP?  Might need some assembly in Mars Orbit, but it's easier to store.

And you might be able to areocapture it into Mars Orbit. Or airbrake to a lower orbit.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/30/2011 11:16 AM
What says you can't send a heatshield via SEP?  Might need some assembly in Mars Orbit, but it's easier to store.

Maybe you could eventually, but not in the near term. NEP is very likely to work eventually. That would be a good idea.

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And you might be able to areocapture it into Mars Orbit. Or airbrake to a lower orbit.

Yes, but then you would still be using chemical propulsion for TMI.
Title: Re: Mars EDL technologies
Post by: kkattula on 01/31/2011 02:31 AM
What says you can't send a heatshield via SEP?  Might need some assembly in Mars Orbit, but it's easier to store.

Maybe you could eventually, but not in the near term. NEP is very likely to work eventually. That would be a good idea.

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And you might be able to areocapture it into Mars Orbit. Or airbrake to a lower orbit.

Yes, but then you would still be using chemical propulsion for TMI.

What the?  You're talking about sending hypergolic propellant to Mars orbit using SEP, but claiming heatshields couldn't be yet?

I'm suggesting the heatshield for EDL (and probably the enitire lander) is sent ahead of time via SEP, along with hypergolic propellant for Earth return. The crew transfer vehicle arrives later using chemical propulsion.

This would be more mass efficient than sending enough extra propellant for propulsive descent. 
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/31/2011 03:26 AM
In the context of a fully reusable lander and relatively cheap propellant in Mars orbit and ISRU propellant on the Martian surface, fully propulsive descent makes sense.

Or, to put it another way, a fully propulsive landing could be refueled on the surface and have about enough delta-v to make orbit (where it could be refueled to come back).

And there's a few possibilities for putting a lot of propellant in LMO in the future:
*Use a modest SEP tug with high exhaust velocity to move a very large full depot from LEO to LMO over the course of several years. This wouldn't require an HLV, especially if you use a dense propellant. 250 tons of propellant could provide ten or so descents for a small fully (or mostly) propulsive lander... say, one just capable of shuttling 3 or 4 crew from orbit to the surface and back.
*ISRU propellant from Phobos? I'm not convinced this is more feasible than the next possibility...
*Orbital atmospheric skimming... Mars is probably the best candidate in the solar system for this technology (Titan would be better because of its lower orbital velocity, but it'd be too far away to be able to use significant solar power). This is ideal because the propellant is located right where you need it (LMO) and would likely be of the same type as made on the surface of Mars (i.e. carbon monoxide and oxygen), allowing the technology for production and propulsion to be similar once it is collected.

That's if it's not feasible to have a fully reusable heatshield that's light enough to allow the whole spacecraft get at least 5km/s propulsive delta-v (first, all the way from the surface to orbit, then a little bit of delta-v at the end for the transition from supersonic to landing). The reusable tiles for the Shuttle require a lot of TLC between missions, something that wouldn't be feasible for Mars. But it would be quite nice to only have to fuel up on the surface of Mars.

A fully reusable lander would also be able to hop suborbitally all over the planet, especially if ISRU equipment is placed at different spots. Heck, it may even be possible to put a very small nuclear power source (super ASRG?) and compact ISRU equipment placed on the lander so that it could visit many different spots on the planet, staying for a month or two until its propellant is replenished, then taking off again to another spot for years on end.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 01/31/2011 03:50 AM
But for landing bulk cargo or large equipment (hab modules, rovers, etc), I agree that fully propulsive landing is inferior to being able to use the Martian atmosphere to do most of your work. In fact, is it feasible to land food and other such bulk supplies at a terminal velocity of 150mph or so? If so, it should be possible to do Martian EDL without any (or very limited thruster use right when reentering) rockets at all once placed on a trajectory intersecting the surface of Mars, though the landing ellipse may be large (it'd take a day trip to pick up the food and stuff). Even so, MER-style landing rockets might make sense to lower the velocity from 150mph to something more practical like 20 or 30 mph.

On the other hand, it'd allow pretty cheap base resupply once water and air are taken care of with ISRU.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 07:44 AM
What the?  You're talking about sending hypergolic propellant to Mars orbit using SEP, but claiming heatshields couldn't be yet?

Small heatshields, sure. But I thought we were talking about large payloads. Propellant is easily divisible, but large heatshields aren't (yet).

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I'm suggesting the heatshield for EDL (and probably the entire lander) is sent ahead of time via SEP, along with hypergolic propellant for Earth return. The crew transfer vehicle arrives later using chemical propulsion.

This would be more mass efficient than sending enough extra propellant for propulsive descent. 

That could be an excellent idea for eventual manned missions. I was looking at it from the perspective of how we could usefully make use of large quantities of propellant in orbit and do so as soon as possible, since that's what I'd like to see in order to stimulate commercial development of small RLVs.
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 08:14 AM
Can anyone point me to a paper detailing All-propulsive edl on mars? I have read i once but cannot locate it. It was interesting because it still used air drag to help slow the vehicle down and this provided a fuel saving.

This is the first one I thought of:

http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf

(Didn't show up on a google search, though, so I had to mine Braun's publication list, which is quite expansive and has some very interesting papers:

http://soliton.ae.gatech.edu/people/rbraun/publications.pdf )

Ah that's the one -thanks. I couldn't remember the conclusion but it seems it's only viable with isp of 650s or more.

I think the most interesting results are the reference trajectories in table 5, which use a partially propulsive landing with no use of any aerosurfaces (parachutes or other drag devices) other than the heat shield.

"Note that in these reference cases, deceleration is accomplished without aeroassist technology elements such as lifting configurations, parachutes, or inflatable aerodynamic decelerators. "

They give a propellant mass fraction of 27.61% for the direct entry case with a descent Isp of 350s (methane/LOX?) and a ballistic coefficient of 477.5kg/m^2.

(they use PMF as payload mass fraction in this table, but also use the more commonly used payload mass fraction further down. It's a bit confusing)

Given those values (you get >50% payload from direct entry to the ground without any aerodynamic devices other than the heat shield, and a very high ballistic coefficient) it's hard to see why anybody is considering anything else...
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 08:17 AM
Given those values (you get >50% payload from direct entry to the ground without any aerodynamic devices other than the heat shield, and a very high ballistic coefficient) it's hard to see why anybody is considering anything else...

To seek and encourage, to the maximum extent possible, the fullest commercial use of space... ;)

But yes, the combined approach is my probable favourite too. You never know what the combination of cheap lift and ISRU might mean though.
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 08:51 AM
That's if it's not feasible to have a fully reusable heatshield that's light enough to allow the whole spacecraft get at least 5km/s propulsive delta-v (first, all the way from the surface to orbit, then a little bit of delta-v at the end for the transition from supersonic to landing). The reusable tiles for the Shuttle require a lot of TLC between missions, something that wouldn't be feasible for Mars. But it would be quite nice to only have to fuel up on the surface of Mars.

It's hard to believe given the current state of NASA, but there has been some progress in heat shield materials development since the shuttle tiles.

And even if you don't what to risk developing a radiatively cooled resuable heat shield, it is certainly possible to build an ablative heat shield out of PICA that could survive a few dozen mars entries. That is commercial off the shelf technology now. And for the near term, it is as good as a reusable heat shield.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 08:53 AM
Or transpiration cooling.
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 09:18 AM
How would that help?

You may need more propellant, but you can transport it more efficiently than with chemical propulsion - unlike a heatshield.

What says you can't send a heatshield via SEP?  Might need some assembly in Mars Orbit, but it's easier to store.

And you might be able to areocapture it into Mars Orbit. Or airbrake to a lower orbit.

I don't get this fascination with SEP for a mars mission. SEP has a huge list of disadvantages compared to good old chemical propulsion for a mars mission. ISP is not everything.

1. SEP does not allow you to use the oberth effect. So instead of less than 1km/s for EML2 to TMI, you need 3 or so.

2. The huge solar cells used for SEP make your spaceship so fragile that it will not be able to use aerocapture or aerobraking. So while the chemical propulsion spacecraft can get from TMI to low mars orbit almost for free by using a heat shield for aerocapture and aerobraking, SEP needs to do this propulsively as well. Another 3km/s.

3. To make 2. worse, SEP does not work very well at mars solar irradiation levels.

4. SEP uses exotic and expensive propellants that will be extremely difficult to manufacture using ISRU. Chemical propulsion just needs water electrolsys, and water has been found everywhere where we have bothered to look thoroughly enough.

5. SEP does not exist on a scale sufficient for a manned mars mission. You would have to scale up existing systems like the DAWN propulsion system by two (decimal) orders of magnitude to make it useful for a manned mars mission. The preferred chemical propulsion system for a mars mission is called a RL-10 and has been in service since 1961. Yes, that is half a century. And it even has been flown in a clustered configuration.

All things added up, you have ~1000m/s for chemical EML2 to LMO (using aerocapture and aerobraking) versus ~6000m/s for SEL EML2 to LMO (fully propulsive).

The only place where SEP could be useful is to get propellant or supplies from LEO to EML2. Even there the benefit is marginal, and it will completely evaporate once we get lunar water for ISRU.

But the last step (EML2-TMI) is best done using chemical propulsion.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 09:44 AM
1. SEP does not allow you to use the oberth effect. So instead of less than 1km/s for EML2 to TMI, you need 3 or so.

True, but because of the higher Isp it still beats chemical propulsion.

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2. The huge solar cells used for SEP make your spaceship so fragile that it will not be able to use aerocapture or aerobraking. So while the chemical propulsion spacecraft can get from TMI to low mars orbit almost for free by using a heat shield for aerocapture and aerobraking, SEP needs to do this propulsively as well. Another 3km/s.

Not almost for free, the heat shield has substantial mass too.

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3. To make 2. worse, SEP does not work very well at mars solar irradiation levels.

Good enough for transporting stuff to Mars orbit.

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4. SEP uses exotic and expensive propellants that will be extremely difficult to manufacture using ISRU. Chemical propulsion just needs water electrolsys, and water has been found everywhere where we have bothered to look thoroughly enough.

SEP may well become much less useful once we have ISRU. But we're a long way away from that. Also note that SEP can use argon, ammonia or hydrazine, which could be produced through ISRU.

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5. SEP does not exist on a scale sufficient for a manned mars mission. You would have to scale up existing systems like the DAWN propulsion system by two (decimal) orders of magnitude to make it useful for a manned mars mission. The preferred chemical propulsion system for a mars mission is called a RL-10 and has been in service since 1961. Yes, that is half a century. And it even has been flown in a clustered configuration.

Agreed, I don't see much use for SEP when it comes to crew transport. Also agreed on RL-10, to which I would add AJ-10. For the foreseeable future cryogens and hypergolics would be better than SEP for crew. In the long term NEP may turn out to be even better.

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The only place where SEP could be useful is to get propellant or supplies from LEO to EML2. Even there the benefit is marginal, and it will completely evaporate once we get lunar water for ISRU.

Not the only place. I see a much bigger role for transporting propellant from EML1/2 to SML1 and LMO, and nearer to home, to GEO, LLO and EMLn/SELn. That propellant could be transported from LEO to EML1/2 by LOX/LH2 propulsion using 3.2km/s three body trajectories, making full use of the Oberth effect, the effiency of LOX/LH2 and advanced trajectories. Note that all of that could be done with existing technology and sometimes existing systems (hypergolic propellant transfer, AJ-10/ R-4D, Dawn thrusters, a single ISS sized solar panel, existing EELV upper stages with straightforward modifications for EOR as described on the ULA website, existing heatshields).

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But the last step (EML2-TMI) is best done using chemical propulsion.

Not according to the numbers I've seen, at least not for propellant.

Just to make this clear: my interest in SEP stems mainly from the fact that it could be used to overcome most of the drawbacks of using hypergolics and avoids the need for HLV-sized heatshields even for landing large payloads on Mars. That means that a properly sized exploration program could start immediately and thus immediately provide a large market for commercial propellant launch services, something I believe will lead to commercial RLVs and then commercial development of space. In other words the combination of SEP and hypergolics will allow us to seek and encourage, to the maximum extent possible, the fullest commercial use of space.

In the longer term I'd expect SEP to be replaced by NEP, and hypergolics by LOX/LH2 and LOX/CH4, both supported by ISRU.
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 10:02 AM
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2. The huge solar cells used for SEP make your spaceship so fragile that it will not be able to use aerocapture or aerobraking. So while the chemical propulsion spacecraft can get from TMI to low mars orbit almost for free by using a heat shield for aerocapture and aerobraking, SEP needs to do this propulsively as well. Another 3km/s.

Not almost for free, the heat shield has substantial mass too.

For a direct entry mars landing mission, you need a heat shield anyway. And even for a more advanced propellant depot based architecture, a heat shield will have lower mass than propellant and be reusable.

I think that a heat shield will be an integral part of a LOX/LH2 based inner solar system space tug.

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4. SEP uses exotic and expensive propellants that will be extremely difficult to manufacture using ISRU. Chemical propulsion just needs water electrolsys, and water has been found everywhere where we have bothered to look thoroughly enough.

SEP may well become much less useful once we have ISRU. But we're a long way away from that. Also note that SEP can use argon, ammonia or hydrazine, which could be produced through ISRU.

But none of the currently operational electric thrusters use one of the above mentioned propellants. So you have another billion dollar development program. A few billion dollars let you launch a lot of chemical propellant even with current launch prices.

Ammonia and hydrazine would have to synthesized using hydrogen, which you would probably get by elecrolyzing water. So you need water anyway. And where do you get the nitrogen?

For chemical propulsion all you need is water, which has been found on the lunar pole and on mars, and is probably present in significant quantities on phobos and deimos.

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5. SEP does not exist on a scale sufficient for a manned mars mission. You would have to scale up existing systems like the DAWN propulsion system by two (decimal) orders of magnitude to make it useful for a manned mars mission. The preferred chemical propulsion system for a mars mission is called a RL-10 and has been in service since 1961. Yes, that is half a century. And it even has been flown in a clustered configuration.

Agreed, I don't see much use for SEP when it comes to crew transport. Also agreed on RL-10, to which I would add AJ-10. For the foreseeable future cryogens and hypergolics would be better than SEP for crew. In the long term NEP may turn out to be even better.

I am not that interested in the long term. Even the things we think of as pretty straightforward such as ACES and propellant depots will take decades at the current pace. I will let the next generation worry about the long term.

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But the last step (EML2-TMI) is best done using chemical propulsion.

Not according to the numbers I've seen, at least not for propellant.

They probably assume fully propulsive MOI and MOI->LMO. That's the only way you can tweak the numbers to make SEL look somewhat competitive :-)
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 10:24 AM
Much agreement, some minor points and one major point below.

For a direct entry mars landing mission, you need a heat shield anyway. And even for a more advanced propellant depot based architecture, a heat shield will have lower mass than propellant and be reusable.

I'm not convinced total IMLEO would be lower, but we can try to look up some numbers. I also have some doubts about the mass fractions in the paper mentioned above, but I'll do some sums first. And yes, I'm thinking in the context of propellant transfer, with a view towards stimulating RLVs.

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I think that a heat shield will be an integral part of a LOX/LH2 based inner solar system space tug.

Perhaps.

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But none of the currently operational electric thrusters use one of the above mentioned propellants. So you have another billion dollar development program. A few billion dollars let you launch a lot of chemical propellant even with current launch prices.

I think 25kW ammonia thrusters do exist, but maybe those are arcjets instead. Your point does have merit, but on the other hand ISRU is long term as well, so if we can dream about ISRU, we can dream about SEP using different propellant.

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Ammonia and hydrazine would have to synthesized using hydrogen, which you would probably get by elecrolyzing water. So you need water anyway. And where do you get the nitrogen?

From the Mars atmosphere.

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For chemical propulsion all you need is water, which has been found on the lunar pole and on mars, and is probably present in significant quantities on phobos and deimos.

I'm all for using water and chemical propulsion where appropriate, I was just pointing out SEP can use ISRU propellants too.

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I am not that interested in the long term. Even the things we think of as pretty straightforward such as ACES and propellant depots will take decades at the current pace. I will let the next generation worry about the long term.

First substantial point I have to make in this post: I agree completely. That's why I'm interested in combining hypergolics and SEP, safely beyond the van Allens (at least initially), restricted to small amounts at a time, avoiding aerobraking beyond what has been demonstrated already. Cheap lift is the one thing we need, and I want to remove all dependencies it has on other technologies and systems, no matter how useful. That includes cryogenic propellant transfer and storage, ACES, aerobraking, ISRU, NEP, surface nuclear power, artificial gravity, bioregenerative life support, let alone things like NTR, variable mixture ratio lox/hydrogen engines, low-g and zero-g oxygen/hydrogen liquefaction and low-g water electrolysis or - goodness forbid - HLVs.

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They probably assume fully propulsive MOI and MOI->LMO. That's the only way you can tweak the numbers to make SEL look somewhat competitive :-)

IIRC the numbers I've seen compared SEP and chemical for transport from EML1/2 to SML1, but I'll have to do some digging as it has been a while.
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 12:46 PM
Much agreement, some minor points and one major point below.

For a direct entry mars landing mission, you need a heat shield anyway. And even for a more advanced propellant depot based architecture, a heat shield will have lower mass than propellant and be reusable.

I'm not convinced total IMLEO would be lower, but we can try to look up some numbers. I also have some doubts about the mass fractions in the paper mentioned above, but I'll do some sums first. And yes, I'm thinking in the context of propellant transfer, with a view towards stimulating RLVs.

I don't really care all that much about IMLEO either. Whatever architecture is chosen for a mars mission, the initial few missions will not be dominated by launch costs to LEO but by R&D and building the payloads. So if you can avoid some R&D at the cost of slightly higher IMLEO I am all for it.

I am pretty sure that you can get lower IMLEO numbers for a SEP based architecture if you use a very high Isp engine. But then you need 10 years or so to get your SEP tug to mars and back, and it will be unusable after one or two trips due to degradation of the solar cells.

A SEP tug will have to use the very best available solar cells to get good power to weight ratio even at mars orbit. And in the quantities required for a space tug these are not cheap even by space standards.

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I think that a heat shield will be an integral part of a LOX/LH2 based inner solar system space tug.

Perhaps.

If I find the time I might do some models on how I think a standard chemical inner solar system tug would look like. But I will finally get my wife and newborn son home from the hospital today, so I am not so sure I will have much free time in the next days... :-)

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But none of the currently operational electric thrusters use one of the above mentioned propellants. So you have another billion dollar development program. A few billion dollars let you launch a lot of chemical propellant even with current launch prices.

I think 25kW ammonia thrusters do exist, but maybe those are arcjets instead.

Yes, I think those are arcjets with a relatively low ISP for electric thrusters (600s or something).

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Your point does have merit, but on the other hand ISRU is long term as well, so if we can dream about ISRU, we can dream about SEP using different propellant.

If there was water on phobos or deimos, using it for ISRU does not have to be that long-term. Space-qualified electrolysis units are commercial off the shelf, and using gaseous hydrogen from electrolysis for a reaction control system will be done on bigelow modules.

Synthesizing nitrogen-based propellants anywhere off-earth on the other hand is very long-term, even if you have a nitrogen source. It is not even that easy on earth. Compare a haber bosch ammonia synthesis reactor to an electolysis unit. And that's the simplest of the nitrogen based propellants to synthesize.

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Ammonia and hydrazine would have to synthesized using hydrogen, which you would probably get by elecrolyzing water. So you need water anyway. And where do you get the nitrogen?

From the Mars atmosphere.

The mars atmosphere is a) very low pressure and b) mostly CO2. Nitrogen content is 2.7%. So extracting nitrogen from it is far from trivial. And on the moon, phobos or deimos you are much more likely to find water than nitrogen-based compounds.

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I am not that interested in the long term. Even the things we think of as pretty straightforward such as ACES and propellant depots will take decades at the current pace. I will let the next generation worry about the long term.

First substantial point I have to make in this post: I agree completely. That's why I'm interested in combining hypergolics and SEP, safely beyond the van Allens (at least initially), restricted to small amounts at a time, avoiding aerobraking beyond what has been demonstrated already. Cheap lift is the one thing we need, and I want to remove all dependencies it has on other technologies and systems, no matter how useful. That includes cryogenic propellant transfer and storage, ACES, aerobraking, ISRU, NEP, surface nuclear power, artificial gravity, bioregenerative life support, let alone things like NTR, variable mixture ratio lox/hydrogen engines, low-g and zero-g oxygen/hydrogen liquefaction and low-g water electrolysis or - goodness forbid - HLVs.

But your architecture does not avoid developing new technologies. You just decide to develop SEP instead of propellant depots. I think that developing SEP at a scale where it would be useful for propellant transfer would be vastly more expensive than developing cryogenic propellant depots. And you still need chemical propulsion for the crew transfer. If you upgrade from hypergolics to LOX/LH2 you can use the chemical propulsion for everything and eliminate a huge development effort for the SEP.

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IIRC the numbers I've seen compared SEP and chemical for transport from EML1/2 to SML1, but I'll have to do some digging as it has been a while.

Going from EML1/2 to SML1 (sun mars L1?) avoids the part where you get the biggest benefit from aerobraking and aerocapture, so it is pretty clear that high Isp propulsion will have an advantage there. I think for a fair comparison you have to consider the propellant mass fraction from EML2 to mars surface or whatever your actual destination is (I think phobos and deimos are interesting destinations on their own, and not just stepping stones to mars).

Anyway, I have to get back to my wife or she will kill me  ;)
Title: Re: Mars EDL technologies
Post by: mmeijeri on 01/31/2011 03:24 PM
If I find the time I might do some models on how I think a standard chemical inner solar system tug would look like. But I will finally get my wife and newborn son home from the hospital today, so I am not so sure I will have much free time in the next days... :-)

Ah, congratulations! I have something to celebrate too, got accepted for a freelance gig today. That means less time for doing unpaid but fun spaceflight related sums and doing both paid and fun sums related to 3d graphics instead. :)
Title: Re: Mars EDL technologies
Post by: rklaehn on 01/31/2011 06:21 PM
If I find the time I might do some models on how I think a standard chemical inner solar system tug would look like. But I will finally get my wife and newborn son home from the hospital today, so I am not so sure I will have much free time in the next days... :-)

Ah, congratulations! I have something to celebrate too, got accepted for a freelance gig today. That means less time for doing unpaid but fun spaceflight related sums and doing both paid and fun sums related to 3d graphics instead. :)

Sounds good. Maybe you can write a kickass 3d computer game, become a multimillionaire, and build rockets in your spare time. In any case, it is a privilege to get paid for something you like to do.
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/01/2011 04:38 AM
Quote from: Nathan
Ah that's the one -thanks. I couldn't remember the conclusion but it seems [fully propulsive landers are] only viable with isp of 650s or more.

That's an interesting paper, but really they tie a couple of hands behind their backs. E.g., they could have modeled a craft with LH2/LO2 propulsion (Isp 450) rather than methane (Isp 350) and one with a titanium hull, rather than a steel hull (able to take 1W/cm2, rather than 0.5 W/cm2). By going with titanium, that ups the payload mass fraction by an extra 4%, and then going with LH2/LO2 reduces propellant mass fraction from ~60% to ~50%, which I guess translates into a 10% boost to payload mass fraction. Thus 8% + 4% + 10% = 22%. Then there is the "margin" factor of 9%. Well what is that really? In practical terms that will translate into residual propellant, which for LH2/LO2 means consumable water for the crew, so it's not a waste. That bumps up the payload mass fraction to 31%. Then there's a missing 4.6%, (their numbers don't add up to 100%). Add that to the mix, you're up to 35.6%. That's really quite close to the spreadsheet I have based on Kirk Sorensen's formulas for a delta v of 4.1 km/sec and using RL-10's (~37%) and an ACES-71 tankage with a slightly beefed up ascender.

That's not bad. That could get you to the surface of Mars basically using an already developed Lunar lander. Martijn should like it, since it uses maximal amounts of propellant, though I suspect he will find a reason to shoot a hole in the idea if for no other reason than I thought of it! ;)
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 02/01/2011 05:07 AM
You're kidding, right? LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher. You can't eat into your margin to achieve better performance. And just because 4.6% is "missing" doesn't mean it is left over and you can magically add it to your PaMF.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 02/01/2011 05:23 AM
Also, I don't think there is enough volume, even within a truncated cone with a 20* backshell angle, for the LH2. I'm not sure there is even enough volume for that much methane/LOX. If there is, there can't be much room left for the payload.
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/01/2011 06:03 AM
1. You're kidding, right? LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust.

2. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher.

3. You can't eat into your margin to achieve better performance.

4. And just because 4.6% is "missing" doesn't mean it is left over and you can magically add it to your PaMF.

5. Also, I don't think there is enough volume, even within a truncated cone with a 20* backshell angle, for the LH2. I'm not sure there is even enough volume for that much methane/LOX. If there is, there can't be much room left for the payload.

1. Huh? Because of the tankage? Maybe you should write the boys at ULA and tell them their Centaur design is all fouled up....

2. I got the 10% reduction in ProMF straight from Figure 11 in March and Braun (2009).

3. Like I said, the margin will simply turn out to be residual propellant--fresh water is useful, therefore the margin is useful payload, and should count as useful payload when calculating the total payload mass fraction. The primary payload in this case the crew and the ascender, plus a few tons of extra cargo. The spread sheet I ran wound up with 8.6 tons of residual propellant. Since the total IMLMO was 93.4 tons, that's 9.24% "margin"--that's pretty close to the 9.74% margin in Marsh and Braun (2009, Table 7). Since all that extra propellant can be used for drinking water, oxygen to breath, electrical energy via fuel cells, that's useful payload.

4. Well, where else would it go? Anyways, adding the missing percentage is consistent with the Sorensen spreadsheet, assuming I did it right (which I think I did, since it's consistent with Zegler et al.'s (2009) figures.)

5. There's room: it's an ACES-71 tank, ~5.5 meters in diameter.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 02/01/2011 06:20 AM
Okay, I'm confused. Are you envisioning an ACES-71, presumably with payload on top, thrusting backwards all the way through Mars' atmosphere from around ~3100m/s orbital velocity until touchdown?
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/01/2011 06:50 AM
Okay, I'm confused. Are you envisioning an ACES-71, presumably with payload on top, thrusting backwards all the way through Mars' atmosphere from around ~3100m/s orbital velocity until touchdown?

The DTAL (Dual Thrust Axis Lander) land horizontally. So the payload's "in front". But yeah, I guess it would have to go backwards, unless they mounted the RL-10's in the middle somehow...

Title: Re: Mars EDL technologies
Post by: Downix on 02/01/2011 06:52 AM
Okay, I'm confused. Are you envisioning an ACES-71, presumably with payload on top, thrusting backwards all the way through Mars' atmosphere from around ~3100m/s orbital velocity until touchdown?

The DTAL (Dual Thrust Axis Lander) land horizontally. So the payload's "in front". But yeah, I guess it would have to go backwards, unless they mounted the RL-10's in the middle somehow...


Yes, it would be going backwards until near the end, when the horiz thrusters would kick in.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 02/01/2011 07:57 AM
Right. But this study assumes a 10m diameter capsule shape - where full aerodynamic drag is preserved even when thrusting - which I assumed meant a truncated cone shape of limited volume. Presumably the engines would also have to be arranged around the periphery of the "heatshield" - or some other exotic configuration - to allow some stability during the retropropulsive maneuvers? (Which makes me wonder whether you will have to protect the craft against potential exhaust impingement?) And of course, you assume that supersonic (and hypersonic?) retropropulsion is viable in the first place?

Also, what happens if the engines are snuffed mid-flight?
Title: Re: Mars EDL technologies
Post by: Nathan on 02/01/2011 08:38 AM
You're kidding, right? LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher. You can't eat into your margin to achieve better performance. And just because 4.6% is "missing" doesn't mean it is left over and you can magically add it to your PaMF.


If the Hydrogen is gelled with 4-5% Methane then the tank size reduces considerably with a hit to ISP of ~30s.

I'm quoting another paper I've read that I cannot find.
Title: Re: Mars EDL technologies
Post by: rklaehn on 02/01/2011 08:47 AM
Right. But this study assumes a 10m diameter capsule shape - where full aerodynamic drag is preserved even when thrusting - which I assumed meant a truncated cone shape of limited volume. Presumably the engines would also have to be arranged around the periphery of the "heatshield" - or some other exotic configuration - to allow some stability during the retropropulsive maneuvers? (Which makes me wonder whether you will have to protect the craft against potential exhaust impingement?) And of course, you assume that supersonic (and hypersonic?) retropropulsion is viable in the first place?

Also, what happens if the engines are snuffed mid-flight?

I think you are mixing two things here. The 10m diameter vehicle with propulsion integrated into the heat shield is for the "reference case" of partially propulsive descent, which is ignored by everybody even though IMHO it makes the most sense.

The idea of partially propulsive descent is to let the atmosphere help you as much as possible without having to add parachutes or other aerodynamic control surfaces other than a simple, vehicle-mounted heat shield.

The whole point of fully propulsive descent is to fully eliminate the heat shield.

See these two statements at the bottom of page 11:

"As offered in this study, a fully-propulsive descent may be used to avoid harsh heating environments usually encountered in atmospheric transit. In this light, the difficulty of developing and employing an enhanced propulsion system is being traded for that of TPS.."

"Throttling authority allows for added control of the vehicle and enables the heat rate limited trajectories which allow elimination of the TPS."
Title: Re: Mars EDL technologies
Post by: mmeijeri on 02/01/2011 08:56 AM
The 10m diameter vehicle with propulsion integrated into the heat shield is for the "reference case" of partially propulsive descent, which is ignored by everybody even though IMHO it makes the most sense.

I have said at least twice that it is my preferred option - apart from the 10m diameter. Restrict it to what will fit inside an EELV fairing (at least 7m), and I'll be happy with it. Replacing as much of the mass as possible with water for transpiration cooling would be even better, as water is just as good for RLVs as propellant.
Title: Re: Mars EDL technologies
Post by: Michael Bloxham on 02/01/2011 08:59 AM
But they still assume the same drag profile as the 10m reference case, don't they? I need to read it again...
Title: Re: Mars EDL technologies
Post by: rklaehn on 02/01/2011 09:05 AM
Also, what happens if the engines are snuffed mid-flight?

It is simply not possible for a typical rocket engine to be snuffed out by the incoming flow. The chamber pressure of a rocket engine designed for operation in the atmosphere is much higher than the stagnation pressure of the supersonic flow.

And the choked flow through the throat of the engine effectively isolates what happens inside the combustion chamber to what happens outside.

We may get some data about firing a rocket engine into a hypersonic flow this year when armadillo and masten start doing boosted hops of their VTVL vehicles to higher altitudes.
Title: Re: Mars EDL technologies
Post by: rklaehn on 02/01/2011 09:52 AM
The 10m diameter vehicle with propulsion integrated into the heat shield is for the "reference case" of partially propulsive descent, which is ignored by everybody even though IMHO it makes the most sense.

I have said at least twice that it is my preferred option - apart from the 10m diameter.

I was not talking about you, but about the discussion in general. Usually it's some rube goldberg device that uses 5 stages of aerodynamic deceleration to avoid any propulsive braking, versus fully propulsive braking with its mass ratio disadvantages.

Quote
Restrict it to what will fit inside an EELV fairing (at least 7m), and I'll be happy with it. Replacing as much of the mass as possible with water for transpiration cooling would be even better, as water is just as good for RLVs as propellant.

I think the 10m diameter design was just a reference design. What matters is the ballistic coefficient, so a 7m vehicle would have to be just 30t instead of the 60t of the reference design. Still plenty for a manned mission with surface rendezvous.
Title: Re: Mars EDL technologies
Post by: rklaehn on 02/01/2011 10:07 AM
But they still assume the same drag profile as the 10m reference case, don't they? I need to read it again...

The way I read it, they just keep the 10m reference case for ease of comparison, and because they have to use some shape. But at the low heat rates they use as limits, that 10m shape might as well look like your typical upper stage, as long as the ballistic coefficient is similar.

By the way, a typical uper stage does have some heat shielding as well to cope with radiative heating by the exhaust and by recirculating exhaust.
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/01/2011 02:40 PM
Quote from: Marsh and Braun
"As offered in this study, a fully-propulsive descent may be used to avoid harsh heating environments usually encountered in atmospheric transit. In this light, the difficulty of developing and employing an enhanced propulsion system is being traded for that of TPS.."

The other thing is you'll save hugely on development costs: on the Moon, aerodynamic deceleration isn't an option, so there is no trade between enhanced propulsion system versus a TPS. Since presumably, we will be going back to the Moon before we launch any manned Mars missions, then the Lunar lander will have to be constructed first. So, the choice is to basically build a single lander that is itself an evolutionary descendant from the Centaur upper stage, or to build two clean sheet designs. The beauty of the fully propulsive lander is that it can land on practically any rocky body in the Solar system, with the exceptions of Earth and Venus.

The other thing is that the fully propulsive lander is easily reused. Isn't it the case that a partially propulsive landing would have to discard the TPS prior to the actual landing?
Title: Re: Mars EDL technologies
Post by: rklaehn on 02/01/2011 03:00 PM
The other thing is that the fully propulsive lander is easily reused. Isn't it the case that a partially propulsive landing would have to discard the TPS prior to the actual landing?

For a partially propulsive lander the engines will have to fire during descent when the heat shield is doing its job. Either through the heat shield, or on the side like the propulsive dragon. You can not let the heat shield cover the engines. So why would you discard the heat shield for landing?

The new vertical landing dragon concept comes pretty close to what a partially propulsive lander would look like, except that it would probably use more efficient pump-fed engines with a decent expansion ratio. The engines would also have to fire straight down to avoid cosine loss.

An ablative PICA heat shield would be able to survive several mars descents, so it would be a waste to throw it away.
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/01/2011 04:20 PM
LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher.
If the Hydrogen is gelled with 4-5% Methane then the tank size reduces considerably with a hit to ISP of ~30s.

I'm quoting another paper I've read that I cannot find.

If you really want a dense, high-thrust propellant, then mix in a little ISRU aluminum into the LO2/LH2 mix.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860018652_1986018652.pdf

1.6 MB pdf

"The specific impulse of the H2/O2 system is only slightly increased by the addition of aluminum. ... However, aluminum is much denser (2700.7 kg/m3 (168.6 lb/ft3)) than beryllium or lithium; therefore, because of the increase in propellant density, significant payload benefits can result from adding aluminum to bipropellant systems. ...Therefore, since the addition of aluminum to H2/O2 results in an increase in propellant density while performance remains essentially constant, significant payload benefits can result..."
Title: Re: Mars EDL technologies
Post by: 93143 on 02/01/2011 08:18 PM
On the other hand, an engine that can handle solid aluminium particles is probably unavoidably much less efficient than, say, an RL-60.  Combined with the other practical issues inherent in metal-loaded triprop systems, I suspect it would turn out to be better to just use biprop...

Of course, the idea should be studied impartially to make sure...  we wouldn't want to dismiss a superior option based on gut instinct alone...
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/02/2011 12:18 AM
There's a long thread here on Al/LO2 propellant. It turns out that probably the best method would be Wickman's who did some experiments mixing Al powder in a gelled liquid oxygen--so it was actually more of a monopropellant. So possibly, you could load this mixture into the oxygen tank of an RL-10 and get it to work....

Actually, the Lunar cold traps are loaded with mercury--and it wouldn't be too hard to extract it; it could literally be distilled. That would give you a dense propellant!
Title: Re: Mars EDL technologies
Post by: RanulfC on 02/02/2011 04:13 PM
Several rather interesting concepts for Mars-EDL:
http://robotics.estec.esa.int/ASTRA/Astra2008/S05/05_03_Lutz.pdf (http://robotics.estec.esa.int/ASTRA/Astra2008/S05/05_03_Lutz.pdf)
http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Papers/Session5/p363.pdf (http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Papers/Session5/p363.pdf)
http://robotics.estec.esa.int/ASTRA/Astra2008/S05/05_02_Graziano.pdf (http://robotics.estec.esa.int/ASTRA/Astra2008/S05/05_02_Graziano.pdf)
http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session5/pr363.pdf (http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session5/pr363.pdf)

Randy
Title: Re: Mars EDL technologies
Post by: guru on 02/04/2011 09:46 PM

It is interesting to me that, as far as I can tell, not a single study has been done to address the question of "how far can heritage EDL tech be pushed?".


I don't have a link to it, and I have not read it, but a reference, or at least a reference to a reference, for such a study is this:

J. Cruz, A. Cianciolo, R. Powell, L. Simonsen, R. Tolson. Entry, descent, and landing technology concept trade study for increasing payload mass to the surface of Mars. Fourth International Symposium on Atmospheric Reentry Vehicles and Systems, Arcachon, France, 2005.

The sentence that references the above study is found in this paper (which I have read):

Ashley M. Korzuna,Gregory F. Dubosa,  Curtis K. Iwataa, Benjamin A. Stahlb, and John J. Quicksallc. A concept for the entry, descent, and landing of high-mass payloads at Mars. Acta Astronautica, Vol. 66, issues 7-8, April-May 2010, pp. 1146-1159.

As the immediately preceding material is copywritten and not openly available, I will forego quoting it directly. But the introduction basically says that, yes, NASA studies have shown that MSL is the limit of what you can do with Viking heritage technology.

(You could probably find this publication at a university library if you don't live too far away from one.  You can also purchase it online. The paper describes a specific method for landing 20 tonnes on Mars, which requires aerocapture, a large diameter aeroshell, an inflatable aerodynamic decelerator, and some retro-propulsive supersonic thrusters (not extensively tested, though some experiments were done by NASA back in the late 60s and early 70s.))

edit: changed hypersonic to supersonic.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 02/04/2011 10:06 PM

It is interesting to me that, as far as I can tell, not a single study has been done to address the question of "how far can heritage EDL tech be pushed?".


I don't have a link to it, and I have not read it, but a reference, or at least a reference to a reference, for such a study is this:

J. Cruz, A. Cianciolo, R. Powell, L. Simonsen, R. Tolson. Entry, descent, and landing technology concept trade study for increasing payload mass to the surface of Mars. Fourth International Symposium on Atmospheric Reentry Vehicles and Systems, Arcachon, France, 2005.

The sentence that references the above study is found in this paper (which I have read):

Ashley M. Korzuna,Gregory F. Dubosa,  Curtis K. Iwataa, Benjamin A. Stahlb, and John J. Quicksallc. A concept for the entry, descent, and landing of high-mass payloads at Mars. Acta Astronautica, Vol. 66, issues 7-8, April-May 2010, pp. 1146-1159.

As the immediately preceding material is copywritten and not openly available, I will forego quoting it directly. But the introduction basically says that, yes, NASA studies have shown that MSL is the limit of what you can do with Viking heritage technology.

(You could probably find this publication at a university library if you don't live too far away from one.  You can also purchase it online. The paper describes a specific method for landing 20 tonnes on Mars, which requires aerocapture, a large diameter aeroshell, an inflatable aerodynamic decelerator, and some retro-propulsive supersonic thrusters (not extensively tested, though some experiments were done by NASA back in the late 60s and early 70s.))

edit: changed hypersonic to supersonic.
Did that paper (which concludes MSL is the limit) actually look at a bipropellant descent stage (with other improvements), a 7 meter diameter heatshield (possible with EELV guppy fairings), and lower altitude landing sites?
Title: Re: Mars EDL technologies
Post by: tnphysics on 02/04/2011 10:26 PM
LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher.
If the Hydrogen is gelled with 4-5% Methane then the tank size reduces considerably with a hit to ISP of ~30s.

I'm quoting another paper I've read that I cannot find.

If you really want a dense, high-thrust propellant, then mix in a little ISRU aluminum into the LO2/LH2 mix.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860018652_1986018652.pdf

1.6 MB pdf

"The specific impulse of the H2/O2 system is only slightly increased by the addition of aluminum. ... However, aluminum is much denser (2700.7 kg/m3 (168.6 lb/ft3)) than beryllium or lithium; therefore, because of the increase in propellant density, significant payload benefits can result from adding aluminum to bipropellant systems. ...Therefore, since the addition of aluminum to H2/O2 results in an increase in propellant density while performance remains essentially constant, significant payload benefits can result..."


Al in LH2-that might allow SSTO from Earth!
Title: Re: Mars EDL technologies
Post by: guru on 02/04/2011 10:51 PM

It is interesting to me that, as far as I can tell, not a single study has been done to address the question of "how far can heritage EDL tech be pushed?".


I don't have a link to it, and I have not read it, but a reference, or at least a reference to a reference, for such a study is this:

J. Cruz, A. Cianciolo, R. Powell, L. Simonsen, R. Tolson. Entry, descent, and landing technology concept trade study for increasing payload mass to the surface of Mars. Fourth International Symposium on Atmospheric Reentry Vehicles and Systems, Arcachon, France, 2005.

The sentence that references the above study is found in this paper (which I have read):

Ashley M. Korzuna,Gregory F. Dubosa,  Curtis K. Iwataa, Benjamin A. Stahlb, and John J. Quicksallc. A concept for the entry, descent, and landing of high-mass payloads at Mars. Acta Astronautica, Vol. 66, issues 7-8, April-May 2010, pp. 1146-1159.

As the immediately preceding material is copywritten and not openly available, I will forego quoting it directly. But the introduction basically says that, yes, NASA studies have shown that MSL is the limit of what you can do with Viking heritage technology.

(You could probably find this publication at a university library if you don't live too far away from one.  You can also purchase it online. The paper describes a specific method for landing 20 tonnes on Mars, which requires aerocapture, a large diameter aeroshell, an inflatable aerodynamic decelerator, and some retro-propulsive supersonic thrusters (not extensively tested, though some experiments were done by NASA back in the late 60s and early 70s.))

edit: changed hypersonic to supersonic.
Did that paper (which concludes MSL is the limit) actually look at a bipropellant descent stage (with other improvements), a 7 meter diameter heatshield (possible with EELV guppy fairings), and lower altitude landing sites?

I am not certain what all the original study looked at, as like I said, I haven't read it.  However, the papers I have read (most especially the second one just referenced) have all stated that we can't do any more with what we have without better heat shield materials, better (as yet undeveloped) parachutes / aerodynamic decelerators, or other technologies.  All of the incremental improvements that can be made with Viking qualified technologies, the studies state, have pretty much been done, and anything bigger requires new qualification programs - the Viking one was very costly to start with, which is why they haven't done any since.

Changing to a bi-propellant landing stage will offer only modest improvements in your landing payload.  It is only used for the last portion of descent after the parachutes have already slowed the craft to subsonic velocities anyway.  For example, MSL has about 300 kg of propellant; dry, the rover + skycrane weigh about 1400 kg.  Even if you replaced the mono-propellant with a bi-propellant you would still only reduce your propellant requirement by about 100 kg for the same amount of deceleration, so you could potentially get 1500 kg instead of 1400 kg.  Adding more propellant than that actually reduces your payload because the Martian atmosphere still has to decelerate that mass.

Larger heatshields mean, necessarily (barring breakthroughs in structural or material sciences) higher ballistic coefficients.  They don't have to scale (correction): times 3/2, but they do still scale somewhat linearly with diameter, as opposed to not at all.  Dropping your ballistic coefficient can actually be somewhat detrimental as entry forces on the MSL are already 12 g's at an entry velocity of 5.9 km/s; reducing the ballistic coefficient would increase the rate of deceleration.  This is one reason why I think it is better to start re-entry from low Mars orbital velocity rather than doing a direct entry - the lower velocity helps to limit the re-entry forces to under 8 g's.

Heating also goes up with the diameter because the Reynold's number increases (unless the velocity decreases), causing the ship to transition to turbulence prior to peak heating.  The increased heating is just a fact of turbulent mechanics.  Current heat shield materials can't handle higher heating loads, and the second paper cited does mention that specifically.

They did plan the 20 tonnes to land at a mean altitude of 0 km, so that was considered.  You could improve on the MSLs landing payload by dropping down to 0 km, as opposed to the 1 km it is slated for, but I don't know how much exactly - I too would be interested to know that.

Title: Re: Mars EDL technologies
Post by: mmeijeri on 02/04/2011 10:55 PM
It is only used for the last portion of descent after the parachutes have already slowed the craft to subsonic velocities anyway.

It doesn't have to, it could start outside the atmosphere. A crasher stage could separate before entering the atmosphere.
Title: Re: Mars EDL technologies
Post by: tnphysics on 02/04/2011 11:20 PM
Who says that the LV fairing, made of suitable material (custom one required), couldn't BE the aeroshell & heatshield? You go in belly first.
Title: Re: Mars EDL technologies
Post by: mmeijeri on 02/04/2011 11:21 PM
Wasn't that the plan for Ares?
Title: Re: Mars EDL technologies
Post by: guru on 02/04/2011 11:37 PM
It is only used for the last portion of descent after the parachutes have already slowed the craft to subsonic velocities anyway.

It doesn't have to, it could start outside the atmosphere. A crasher stage could separate before entering the atmosphere.

Yes, it could. I would love it if it did. But I think, in this instance, he was just talking about the landing stage post parachute deployment like how its currently done.

The method you suggest (firing through re-entry) is not as mass efficient as the mostly aerodynamic method currently used, but I don't personally have a huge problem with that deficiency.

As a tax-payer, I could pay for two more launches of an HLV for extra propellant (which might be available in ten year, and if you pay for one launch a year, you're basically paying for five anyway due to fixed costs) and use propulsive deceleration.  Or I could sit around for 10 years waiting for larger arcjet chambers and parachute test facilities to be built and used so I could test bigger heat shields, parachutes, and retro-propulsors in experimentally relevant conditions, and then actually launch ten years after that...

On the other hand, a bigger arcjet test facility would be totally awesome.

On the third hand, there's also no guarantee that I wouldn't sit around waiting 20 years for an HLV.

On the fourth hand, it might be possible to have propellant depots up and running in less than ten years, so we would need neither an HLV nor advanced aerodynamic deceleration methods.

Who knows?

Title: Re: Mars EDL technologies
Post by: guru on 02/05/2011 12:38 AM
Who says that the LV fairing, made of suitable material (custom one required), couldn't BE the aeroshell & heatshield? You go in belly first.

Using an elongated biconic re-entry vehicle is a great way to increase the landable mass, but, there's a reason every Mars EDL system that's ever been built is in the shape of a 70 degree cone - it's the only shape that's ever been qualified.  Those types of programs are expensive, but they should be done.

Heavier payloads are still going to require larger parachutes or supersonic retro-propulsion, though, so the help from the better aeroshell is actually still insufficient.  Scientists are not quite sure how to test larger parachutes than they already have for a Martian environment.  Super-sonic retropropulsion might wind up being easier, but the propellant for that is going to weigh a lot more than a parachute.

It's all a tradeoff.

So that's a good question.  What is the best metric for determining the success of a Mars EDL system.  Is it dollars/kg on the surface, assuming all other metrics are met, or is there something else that we should consider?  Could we look and say that the largest payload fraction would be the best metric, as that would keep launch costs and hardware production costs down?  I don't know.  I think this thread has gone pretty far into the "how's" of getting to the surface, but we haven't stopped and asked what all of the requirements are (programatic, financial, ergonomic, safety, etc.).
Title: Re: Mars EDL technologies
Post by: Robotbeat on 02/05/2011 12:45 AM
Who says that the LV fairing, made of suitable material (custom one required), couldn't BE the aeroshell & heatshield? You go in belly first.

Using an elongated biconic re-entry vehicle is a great way to increase the landable mass, but, there's a reason every Mars EDL system that's ever been built is in the shape of a 70 degree cone - it's the only shape that's ever been qualified.  Those types of programs are expensive, but they should be done.

Heavier payloads are still going to require larger parachutes or supersonic retro-propulsion, though, so the help from the better aeroshell is actually still insufficient.  Scientists are not quite sure how to test larger parachutes than they already have for a Martian environment.  Super-sonic retropropulsion might wind up being easier, but the propellant for that is going to weigh a lot more than a parachute.

It's all a tradeoff.

So that's a good question.  What is the best metric for determining the success of a Mars EDL system.  Is it dollars/kg on the surface, assuming all other metrics are met, or is there something else that we should consider?  Could we look and say that the largest payload fraction would be the best metric, as that would keep launch costs and hardware production costs down?  I don't know.  I think this thread has gone pretty far into the "how's" of getting to the surface, but we haven't stopped and asked what all of the requirements are (programatic, financial, ergonomic, safety, etc.).
Heavier? Define Heavier. 2 tons payload? 3 tons? 5?
If we can land 5 tons of usable hardware on to the surface within a few miles of the same spot, along with a crane/rover vehicle which could move the elements to the right spot, we could build all the elements we need for a Mars base. 5 tons of dry mass may even be enough for an ascent spacecraft if you use ISRU propellant.

Besides the ascent vehicle, even just 3 tons would be enough for the pieces of a Mars base. It'd be a significant difficulty to integrate all the elements with such a small mass, but it'd be doable especially for just supply pallets.
Title: Re: Mars EDL technologies
Post by: guru on 02/05/2011 04:05 AM

Heavier? Define Heavier. 2 tons payload? 3 tons? 5?
If we can land 5 tons of usable hardware on to the surface within a few miles of the same spot, along with a crane/rover vehicle which could move the elements to the right spot, we could build all the elements we need for a Mars base. 5 tons of dry mass may even be enough for an ascent spacecraft if you use ISRU propellant.

Besides the ascent vehicle, even just 3 tons would be enough for the pieces of a Mars base. It'd be a significant difficulty to integrate all the elements with such a small mass, but it'd be doable especially for just supply pallets.

By heavier, I mean anything heavier than than the MSL/skycrane system.  If you can slow down to lower than Mach 2.1 before chute deployment, then, yes, you can probably handle slightly larger payloads with the same chute (I don't know exactly how much), but you will have a higher terminal velocity in that case.  That means that you will need more propellant (or, actually, maybe just better propellant) in the landing stage to cover the increased delta -V requirement.  It's possible, but I still don't think you would get more than about 2.5 tonnes out of it all told.

As always, I could be wrong.
Title: Re: Mars EDL technologies
Post by: tnphysics on 02/06/2011 01:42 AM
LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher.
If the Hydrogen is gelled with 4-5% Methane then the tank size reduces considerably with a hit to ISP of ~30s.

I'm quoting another paper I've read that I cannot find.

If you really want a dense, high-thrust propellant, then mix in a little ISRU aluminum into the LO2/LH2 mix.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860018652_1986018652.pdf

1.6 MB pdf

"The specific impulse of the H2/O2 system is only slightly increased by the addition of aluminum. ... However, aluminum is much denser (2700.7 kg/m3 (168.6 lb/ft3)) than beryllium or lithium; therefore, because of the increase in propellant density, significant payload benefits can result from adding aluminum to bipropellant systems. ...Therefore, since the addition of aluminum to H2/O2 results in an increase in propellant density while performance remains essentially constant, significant payload benefits can result..."


This is by raising density-easier to use LCH4
Title: Re: Mars EDL technologies
Post by: Nathan on 02/06/2011 02:36 AM
LH2/LO2 propulsion will have a higher dry mass fraction for the same amount of thrust. You won't achieve a 10% decrease in ProMF if the final dry mass of the system is higher.
If the Hydrogen is gelled with 4-5% Methane then the tank size reduces considerably with a hit to ISP of ~30s.

I'm quoting another paper I've read that I cannot find.

If you really want a dense, high-thrust propellant, then mix in a little ISRU aluminum into the LO2/LH2 mix.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860018652_1986018652.pdf

1.6 MB pdf

"The specific impulse of the H2/O2 system is only slightly increased by the addition of aluminum. ... However, aluminum is much denser (2700.7 kg/m3 (168.6 lb/ft3)) than beryllium or lithium; therefore, because of the increase in propellant density, significant payload benefits can result from adding aluminum to bipropellant systems. ...Therefore, since the addition of aluminum to H2/O2 results in an increase in propellant density while performance remains essentially constant, significant payload benefits can result..."


This is by raising density-easier to use LCH4
A small amount of ch4 in the h2 also reduces boil-off.
Title: Re: Mars EDL technologies
Post by: Warren Platts on 02/07/2011 03:15 PM
This is by raising density-easier to use LCH4

I see what you're saying, but the beauty part of Al is that you actually get a marginal bump in your Isp.
Title: Re: Mars EDL technologies
Post by: guru on 03/21/2011 02:32 AM
Question:

Could a viking-style entry vehicle, designed for the martian entry environment, theoretically also work sufficiently well at earth-entry?

I'm thinking it might; as presumably you can just open the chutes at an earth altitude analogous to that which they are designed for deploying at mars, right?


I was doing some "research" (i.e. killing time reading Encyclopedia Astronautica) a little while ago when I stumbled on an entry that reminded me of your question.  Apparently, back in the 1980's, NASA looked at the possibility of using a viking heat shield as an emergency crew escape system from the Space Station.  The system was called SCRAM (Station Crew Return Alternative Module), and is briefly mentioned here. 

http://astronautix.com/craft/nasaacrv.htm

The g-forces were a little high, but survivable.  As for the parachute,  I don't think the one designed for Mars would survive in Earth's much denser atmosphere.  However, if you are using the craft as your primary means of abort, a second parachute could be stowed for use at Earth.  The mass penalty for the second chute would be acceptable, I should think.
Title: Re: Mars EDL technologies
Post by: Norm38 on 08/05/2012 12:08 AM
Moved this post to a more appropriate thread:

Regarding the "7 launch NTR Mars Mission" plan, focusing JUST on the EDL sequence starting at 2:25...

Link( youtube /watch?v=uUBhn3_P3hU)

Aerobraking, hypersonic parachutes and retrorockets all are used in this approach. Is this a realistic or completely unrealistic scaling up of the current state of the art.  Can we actually build something of this scale?
Title: Re: Mars EDL technologies
Post by: guru on 02/12/2013 04:44 PM
Quote
Moved this post to a more appropriate thread:

Regarding the "7 launch NTR Mars Mission" plan, focusing JUST on the EDL sequence starting at 2:25...

Link( youtube /watch?v=uUBhn3_P3hU)

Aerobraking, hypersonic parachutes and retrorockets all are used in this approach. Is this a realistic or completely unrealistic scaling up of the current state of the art. Can we actually build something of this scale?

Short answer, no.

DRM 5.0, which the video is based on, doesn't use hypersonic parachutes or aerobraking as you described, though.  It does use aerocapture (which is harder than state of the art aerobraking, and is still untested) and supersonic retropropulsion (also puzzlingly untested given its relative simplicity to at least try).  The parachutes, if they are even used in the DRM, would be deployed in the low supersonic or subsonic regime, and thus fall within the state of the art (unless they are supersonic and larger than, I think, 19 m in diameter).

The EDL sequence as a whole, though, is not a scaling of the state of the art - it requires an expansion of it for most phases shown.
Title: Re: Mars EDL technologies
Post by: guru on 02/12/2013 05:25 PM
And, as long as I have reopened the thread, I would like to point out how exciting some of the work being done at NASA in regards to Mars EDL.

For starters, there are the widely publicized projects of HIAD, which has successfully tested subscale hypersonic inflatable heat shields on suborbital flights, and ALHAT, which has flown (and also, sadly, crashed) the rocket powered Morpheus vehicle in order to test new landing algorithms.  They are building a new Morpheus style vehicle and continue to test their landing sensors and control algorithms with a helicopter.

I noticed two other exciting projects while perusing NASA's Strategic Space Technology Investment Plan yesterday that I was only vaguely aware of until now. The first is the Low Density Supersonic Decelerators project, which is developing inflatable heat shield extensions and 30 meter diameter supersonic parachutes.  This is planned to give NASA the ability to land probes with a mass of up to 3 tonnes (double the current state of the art) on Mars by 2020.  This is the first qualification program of new Mars EDL technology since the Viking program in the 1970s!

The other project is the Deployable Aeroshell Concepts and Conformal TPS project, which is developing materials and structures for a folding heat shield of woven carbon fabric.  From the projects NASA website:  "The combination of low ballistic coefficient, high thermal protection capability allows for lower entry flight path angle and as a result, ADEPT concept has been shown to be capable of achieving very low entry g-loads for mission such as robotic Venus, Mars, and Saturn."  This is highly applicable to future manned missions, which would require the large heat shield diameters made possible by folding.

Here is a link to a video showing a test of the Low Density Supersonic Decelerators project's inflatable heat shield extension on a rocket sled done early last year:

http://www.youtube.com/watch?v=OQl_ZMKAZ-I
Title: Re: Mars EDL technologies
Post by: Kaputnik on 02/12/2013 07:33 PM
Thanks, was not aware of this work being done. Exciting stuff :)
Title: Re: Mars EDL technologies
Post by: JohnFornaro on 02/13/2013 01:14 PM
Using an elongated biconic re-entry vehicle is a great way to increase the landable mass, but, there's a reason every Mars EDL system that's ever been built is in the shape of a 70 degree cone - it's the only shape that's ever been qualified.

I thought it was the best shape for the atmo.  But still, if there's ever to be manned landings, habitats, excavators and such, they've gotta be able to land some tonnage.

If five tons is the practicable limit, then any colonization effort would seem to be doomed from the start.  Such a vehicle could only land what, one person at a time?

So... got any pix of the elongated biconic re-entry vehicle that could do the job?
Title: Re: Mars EDL technologies
Post by: manboy on 02/13/2013 03:17 PM
This is planned to give NASA the ability to land probes with a mass of up to 3 tonnes (double the current state of the art) on Mars by 2020.
I thought the current limit was a single tonne.
Title: Re: Mars EDL technologies
Post by: guru on 02/13/2013 06:11 PM
This is planned to give NASA the ability to land probes with a mass of up to 3 tonnes (double the current state of the art) on Mars by 2020.
I thought the current limit was a single tonne.

I included the mass of the landing stage in the current state of the art as it is also decelerated to zero velocity at some point near to the Martian surface, but, you're right, in an apples to apples comparison that mass wouldn't be included, and thus, three tonnes is triple the current state of the art.

By that same token, if the landing stage mass was integrated into a future three tonne primary payload and reused as part of the ascent system, then the landed useful mass could be more like 4 or 5 tonnes.
Title: Re: Mars EDL technologies
Post by: guru on 02/13/2013 06:35 PM

So... got any pix of the elongated biconic re-entry vehicle that could do the job?

Since one hasn't been built for this particular purpose, no, but real and imagined examples of biconic and even tri-conic vehicles are the NASA DRM 5.0  entry capsules (which, as mentioned, would require either better retropropulsion or deployable aerodynamic decelerator technology than we have now), Blue Origin's space vehicle (granted, it's not elongated), the DC-X vehicle and its previously anticipated follow-ons, and a few old warheads, such as the Mk 6.

One of my favorite images of a biconic vehicle (which also looks like it was designed for earth entry), which was done by John Frassanito & Associates, can be found at the following link:

http://www.frassanito.com/work/images/planning02.jpg
Title: Re: Mars EDL technologies
Post by: Kaputnik on 02/13/2013 09:40 PM
Or there's these ones from the 80s...

http://www.marshome.org/images2/albums/Exploration%20and%20Settlement%20of%20Mars/Conceptual%20Structures/Temporary%20Earth%20Imported%20Structures/9_landing_0.jpg (http://www.marshome.org/images2/albums/Exploration%20and%20Settlement%20of%20Mars/Conceptual%20Structures/Temporary%20Earth%20Imported%20Structures/9_landing_0.jpg)
Title: Re: Mars EDL technologies
Post by: simcosmos on 02/14/2013 09:50 PM
I also like biconics (and Conceptual Missions Designs)... or something similar...

Sharing a quick animated gif, with outdated graphics (basic shape, non textured) of a custom conceptual Mars entry vehicle brainstorm. High lift (hopefully... no wind tunnel), +/- flat bottom, no parachutes / no separation / minimum reconfiguration events, internal cargo cylinder with a diameter of ~5m up to 6m, (depending of iteration); study of HLV integration (you may look at it as an SLS block II, although I started these musings before SLS and even before Constellation) and several TMI strategies; cargo & mission hardware interaction and integration vs propulsion, power, entry, landing and other requirements, etc impacts on the entry vehicle's shape / internal layout and so on and so on...

Maybe one day will gather some of the conceptual notes and open a separated thread: it may result in an interesting topic for the Mars or the Advanced Concepts section (at least from some integration aspects and from the visual eye-candy perspective, if I ever update the 3D stuff to more properly represent the ideas)...

Ho, and I call it Mars Dropship ;)

António Maia
(back to lurker mode)
Title: Re: Mars EDL technologies
Post by: JohnFornaro on 02/15/2013 01:38 AM

So... got any pix of the elongated biconic re-entry vehicle that could do the job?

One of my favorite images of a biconic vehicle (which also looks like it was designed for earth entry), which was done by John Frassanito & Associates, can be found at the following link:

http://www.frassanito.com/work/images/planning02.jpg

Thanks.  That's substantially more than a five ton landing vehicle.  What about wings? how is it stabilized?
Title: Re: Mars EDL technologies
Post by: JohnFornaro on 02/15/2013 01:40 AM
Antonio.  Your GIF there is a mite too fast for these old eyeballs.
Title: Re: Mars EDL technologies
Post by: manboy on 02/15/2013 04:50 AM
Antonio.  Your GIF there is a mite too fast for these old eyeballs.
http://www.gifexploder.com/exploderesults.aspx?fn=nasa_vse_sc_devwip20130214simcosmos_marsdropship.gif
Title: Re: Mars EDL technologies
Post by: guru on 02/22/2013 05:51 PM

Thanks.  That's substantially more than a five ton landing vehicle.  What about wings? how is it stabilized?

I suppose I should clarify that when I said "also designed for Earth", I meant that it was "also" like the DC-X follow on or Blue Origin's capsule, not that it was (necessarily) designed for Mars in addition to Earth.

Yes, something like that would probably weigh closer to 15 or 20 tonnes looking at it.

It has no wings.  Biconics create some lift by flying at an angle (and some are shaped asymmetrically to produce lift at alpha = 0), and have a higher lift to drag ratio that a standard capsule.  I'm not familiar with the background of the image and I can't find any references to it other than the website the image is posted on, I just like the visual presentation of it.  However, from the image, it is at least clear that there are attitude thrusters located in the nose.  Other biconic designs I have seen have flaps at the back.
Title: Re: Mars EDL technologies
Post by: guru on 05/17/2013 10:58 PM
NTRS is back up again! - mostly.  I found a recent paper describing some small scale testing that NASA is (still hopefully - with sequestration, you never know) planning to carry on supersonic retro-propulsion in a one-foot by one-foot wind tunnel.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130000774_2012019438.pdf
Title: Re: Mars EDL technologies
Post by: guru on 06/21/2013 06:29 PM
This isn't new, but I stumbled on a 2005 presentation made by Steve Lingard of Vorticity Ltd that gives a good overview of supersonic parachute technology, with particular attention paid to the Huygens Titan lander parachute.

After reading through it, I find myself wondering why it's so hard (aside from the actual flight costs) to qualify a 30 meter diameter Mach 3 parachute for Mars landings.  It looks like inflatable deceleration devices have been deployed with diameters of up to 60 meters and at speeds up to Mach 10 in Earth's vastly thicker (and thus probably hotter) atmosphere.

The presentation is attached, or you can download it directly from the link.

http://www.mrc.uidaho.edu/~atkinson/IPPW/IPPW-3/Parachute%20Course%20Material/11%20-%20Supersonic%20parachutes%20Lingard.pdf
Title: Re: Mars EDL technologies
Post by: simonbp on 06/21/2013 07:19 PM
It looks like inflatable deceleration devices have been deployed with diameters of up to 60 meters and at speeds up to Mach 10 in Earth's vastly thicker (and thus probably hotter) atmosphere.

You mean the ballute? It's been tested, but IIRC, there were issues with reliability.

What has been been tested very successfully is the IRVE line from NASA Langley: http://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/irve3-success.html
Title: Re: Mars EDL technologies
Post by: guru on 06/23/2013 02:17 AM
No, actually, I didn't mean a ballute exclusively.  There were multiple options shown that fit the specific application mentioned in the slides for landing heavy payloads on Mars (Mach 3 deployment capability).  The point was that deceleration devices exist that can withstand heat and aerodynamic forces and still work at even higher velocities.

The IRVE is just a clamped ballute, and being front facing it presents issues for separation during atmospheric flight.

Parachutes are actually more efficient at lower mach numbers.
Title: Re: Mars EDL technologies
Post by: Proponent on 06/28/2013 05:14 AM
This probably a dumb question, but why did Huygens need a supersonic parachute?  I'd think that in Titan's dense atmosphere the terminal speed of the the Huygens capsule itself, without any 'chutes, would have been subsonic.  Was it impractical for some reason to make the capsule aerodynamically stable without a 'chute?
Title: Re: Mars EDL technologies
Post by: Robotbeat on 06/28/2013 06:09 PM
This probably a dumb question, but why did Huygens need a supersonic parachute?  I'd think that in Titan's dense atmosphere the terminal speed of the the Huygens capsule itself, without any 'chutes, would have been subsonic.  Was it impractical for some reason to make the capsule aerodynamically stable without a 'chute?
Kinda wondering the same thing.
Title: Re: Mars EDL technologies
Post by: R7 on 06/28/2013 11:11 PM
why did Huygens need a supersonic parachute?  I'd think that in Titan's dense atmosphere the terminal speed of the the Huygens capsule itself, without any 'chutes, would have been subsonic.

Wild guess: because slowing down as early as possible enabled better scientific measurements?
Title: Re: Mars EDL technologies
Post by: spectre9 on 06/29/2013 03:28 AM
The descent was over 2 hours.

The idea being that the probe could take plenty of images on the way down.

Now we know exactly how hazy it is.
Title: Re: Mars EDL technologies
Post by: Dalhousie on 07/01/2013 01:43 AM
The descent was over 2 hours.

The idea being that the probe could take plenty of images on the way down.

Now we know exactly how hazy it is.

The lower atmosphere is very clear and Huygens got some great descent images.  They are still the only oblique aerial photos we have of another body in the solar system.

Title: Re: Mars EDL technologies
Post by: Nydoc on 09/08/2013 06:52 AM
DRM 5.0, which the video is based on, doesn't use hypersonic parachutes or aerobraking as you described, though.  It does use aerocapture (which is harder than state of the art aerobraking, and is still untested) and supersonic retropropulsion (also puzzlingly untested given its relative simplicity to at least try).
I found some research is being done at Langley:
http://youtube.com/watch?v=i-coJg_vgxI
Title: Re: Mars EDL technologies
Post by: SaxtonHale on 10/01/2013 03:07 AM
DRM 5.0, which the video is based on, doesn't use hypersonic parachutes or aerobraking as you described, though.  It does use aerocapture (which is harder than state of the art aerobraking, and is still untested) and supersonic retropropulsion (also puzzlingly untested given its relative simplicity to at least try).
I found some research is being done at Langley:

Great video. Looks like larger vehicles are going to have serious side heating unless they can tuck themselves into a raindrop shape (yes, I know raindrops are spheres)

The boundary layer at 14:00 (http://youtu.be/i-coJg_vgxI?t=14m (http://youtu.be/i-coJg_vgxI?t=14m)) looked especially magnificent. Hard to imagine what the current imagined (concept art) Super Draco configuration would look like in this setup.
Title: Re: Mars EDL technologies
Post by: guru on 10/04/2013 03:44 PM
Over on the disussion thread in the Spacex General section for the following article,

http://www.nasaspaceflight.com/2013/10/musk-plans-reusability-falcon-9-rocket/

it was pointed out by guckyfan that the article states that supersonic retropropulsion (SSRP) was achieved with SpaceX's last launch, and this seems like a more appropriate thread to discuss this if anyone is interested.  This is a big deal because SSRP is a major enabling technology for landing heavy payloads on Mars and had not been tested (openly) prior to this launch.

I understand that the Falcon 9 V 1.1 first stage separates from the second stage moving at about Mach 6 (based on speed of sound at sea level), whereas a regular first stage might be moving closer to Mach 10.  On Mars, while the speed of sound is different, the Mach number is still a critical parameter for retro-propulsion (though the Reynold's number and ballistic coefficient, among others, matter for drag and heat transfer).  A typical Mars probe will slow to about Mach 2 with just a heat shield, but a heavier manned vehicle will probably only get down to a terminal velocity of around Mach 5 or 6, and that would be down in the lower parts of Mars' atmosphere, which is within the range applicable to the SpaceX Cassiope launch.

I'm curious about the Falcon vehicle's aerodynamics, or rather the effects of the thrusting on the aerodynamics.  Is the thrust coefficient for the three engines great enough that they just blast the boundary layer away from the lower side of the rocket so they don't have to worry as much about shock wave interactions?  (Is that question even an accurate statement of the physics involved?)  If not, what types of models (physical or numerical) did they use to characterize the fluid/plasma mechanics over the course of the reentry?

I can see this event having a major effect on the planning for future Mars EDL systems, both manned and unmanned.

(As an aside, my own amateur models show that using constant thrust and an appropriately sized propulsion system somewhat optimized both for mass and deceleration rates, and allowing for supersonic retro-propulsion, a vehicle using direct entry at Mars would hit the atmosphere at the 100 km mark moving at about Mach 7, while an entry starting from a 130 km orbit would hit at about Mach 9.  The reason that number is lower for the direct entry is that on a direct entry, you can begin thrusting at a much higher altitude, generally somewhere between 2,000 and 4,000 km.  The velocity can be much lower than that, even sub-sonic, but the payload goes down as a result.  SpaceX's test may not apply to such a fully propulsive landing, but certainly fits within a combined aero/propulsive descent architecture.)
Title: Re: Mars EDL technologies
Post by: catdlr on 12/18/2013 03:24 AM
JPL to Test New Supersonic Decelerator Technology

LDSD Packed Parachute A 100-foot diameter packed-parachute, bridles and lines are readied into position for a Low Density Supersonic Decelerator (LDSD) test that occurred at the U.S. Naval Air Weapons Station at China Lake earlier this year. A similar packed parachute in both size and material will be used at the mesa test on Dec 18, 2013 at JPL. Credit: NASA/JPL-Caltech

December 17, 2013

A giant crane will tower above NASA's Jet Propulsion Laboratory in Pasadena, Calif., shooting out of a hilly mesa like an oversized erector set, ready to help test components of NASA's Low Density Supersonic Decelerator (LDSD) project. The goal of the challenging technology, led by JPL, is to enable a future mission to Mars or other planetary bodies that uses heavier spacecraft and lands them at locations that were previously not achievable.

The crane-test is scheduled for tomorrow, Dec. 18, weather permitting. The test will simulate the acceleration of a large parachute being pulled away from a spacecraft. The purpose of the test is to show that all of the parachute lines and bridles come out in an organized manner and do not catch on other vehicle hardware as they are deployed.

Validation tests are crucial to working out the kinks before a system of this type is used for future space missions. During this test, the parachute, which has a diameter of roughly 100 feet (30.5 meters), will not open. Its size is a significant upgrade by comparison to parachutes that have come before it. For instance, last year's successful landing of NASA's Mars Curiosity Rover utilized a parachute that measured only 51 feet (15.5 meters) across, about half the size.

The heavier planetary landers of the future require much larger drag devices than any now in use to slow them down -- and those next-generation drag devices will need to be deployed at higher supersonic speeds to safely land a vehicle, plus crew and cargo for potential human missions.

Current Mars landing techniques date back to NASA's Viking mission, which put two landers on Mars in 1976. That mission's basic parachute design has been in use ever since, with additional landing technologies, and was used again in 2012 to deliver the Curiosity rover to Mars. To conduct more massive exploration missions in the future, however, NASA must advance the technology to a new level of sophistication.

Testing for the LDSD project began in 2012 at the U.S. Navy's China Lake Naval Air Weapons Station in California and will be conducted through 2015.

In the next few years, the Low Density Supersonic Decelerator Technology Demonstration Mission will conduct full-scale, stratospheric tests of these breakthrough technologies high above Earth to prove their value for future space exploration missions.

More information about LDSD is at: http://www.nasa.gov/mission_pages/tdm/ldsd/#.UqsZZGRDt9k .

David Israel 818-354-4797
Jet Propulsion Laboratory, Pasadena, Calif.
[email protected]
Title: Re: Mars EDL technologies
Post by: AJA on 01/31/2014 03:25 AM

Video of a chopper dropped, sled accelerated parachute deployment test. (via @marsroverdriver (https://twitter.com/marsroverdriver/status/429071041818669056))

https://www.youtube.com/watch?v=xQCgs6Upu_E


4:24...


(http://4.bp.blogspot.com/-DK3UQwP7DKQ/Tw4pqZBilQI/AAAAAAAAAm0/tCgFmiUgDRs/s1600/neil-degrasse-tyson-badass-gif.gif)


This is why Mars can't have nice things.
Title: Re: Mars EDL technologies
Post by: Kaputnik on 02/07/2014 07:30 AM
the parachute, which has a diameter of roughly 100 feet (30.5 meters), will not open. Its size is a significant upgrade by comparison to parachutes that have come before it. For instance, last year's successful landing of NASA's Mars Curiosity Rover utilized a parachute that measured only 51 feet (15.5 meters) across, about half the size.

'Size' is such an ambiguous word. By the metric that actually matters, the parachute is four times the size of Curiosity's.

Seriously, though, great to see progress on a new generation of supersonic decelerators.
Title: Re: Mars EDL technologies
Post by: catdlr on 04/03/2014 08:25 PM
Media Invited to View NASA Cutting-edge Landing Technology Before Test Flight

April 3, 2014
RELEASE
Media Invited to View NASA Cutting-edge Landing Technology Before Test Flight

NASA's Low-Density Supersonic Decelerator (LDSD) project will be flying a rocket-powered, saucer-shaped test vehicle into near-space this June from the U.S. Navy's Pacific Missile Range Facility on Kauai, Hawaii.

Media are invited to NASA's Jet Propulsion Laboratory (JPL) on Wednesday, April 9, for a brief mission overview and visit to the clean room where this near-space experimental test vehicle is being prepared for shipment to Hawaii. The mission overview and tour will take place from 10 a.m. to 12:30 p.m. PDT at JPL, located at 4800 Oak Grove Drive, Pasadena, Calif., off the Berkshire/ Oak Grove off-ramp of the 210 Freeway.

The LDSD crosscutting demonstration mission will test breakthrough technologies that will enable large payloads to be safely landed on the surface of Mars, or other planetary bodies with atmospheres, including Earth. The technologies will not only enable landing of larger payloads on Mars, but also allow access to much more of the planet's surface by enabling landings at higher altitude sites.

Interview opportunities for members of the LDSD team will be offered after both the briefing on the project in JPL's von Karman auditorium and in the "High Bay 2" clean room where the saucer-shaped craft currently resides.
Journalists who would like to attend the event must arrange access in advance by emailing JPL Media Relations' Elena Mejia at [email protected] by 11 a.m. PDT Tuesday, April 8. Valid media credentials are required. Non-U.S. citizens also must bring a valid passport. Detailed instructions will be given to media who RSVP about the options for entering the clean room or viewing from a gallery. Media in the clean room must wear flat, closed-toe shoes and long pants and will be required to don special outerwear and have any recording equipment cleaned.

More information about the LDSD space technology demonstration mission is online at:
http://www.nasa.gov/mission_pages/tdm/ldsd/

For a diagram of the proposed test, see page three right column from this document:

http://www.nasa.gov/pdf/737628main_Final_LDSD_Fact_Sheet_3-26-13.pdf
Title: Re: Mars EDL technologies
Post by: Kaputnik on 04/03/2014 09:38 PM
A question: are these inflatable decelerators compatible with lifting/guided entry, or must they be symmetrically loaded?
Title: Re: Mars EDL technologies
Post by: catdlr on 04/11/2014 03:31 AM
an explanation to the video posted above.

LDSD: We Brake for Mars

Published on Apr 9, 2014
NASA tests a supersonic parachute under Mars-like conditions for future exploration.


https://www.youtube.com/watch?v=9h1NtQJ59kM
Title: Re: Mars EDL technologies
Post by: catdlr on 04/11/2014 03:42 AM
NASA wants to land something big on Mars: Will a flying saucer help?

http://www.latimes.com/science/sciencenow/la-sci-sn-nasa-ldsd-flying-saucer-20140409,0,2628305.story

Quote
In a few days, the agency will move the vehicle from the clean room at JPL where it is being built to the Navy's Pacific Missile Range Facility in Hawaii. There, in the first week of June, it will be carried to an altitude of 120,000 feet by a giant balloon. Then rockets on the vehicle will take over, pushing it to an altitude of 180,000 feet and helping to reach supersonic speeds. The thin atmosphere at this altitude is similar to the thin atmosphere on Mars.

photo credit: Mel Melcon / Los Angeles Times
Title: Re: Mars EDL technologies
Post by: vulture4 on 04/17/2014 09:37 PM
Armadillo used an inflatable decellerator on the STIG; it seems to have worked pretty well.
Title: Re: Mars EDL technologies
Post by: Blackstar on 04/26/2014 10:25 PM
I'm wondering if there is anything more extensive on this. I'm only finding a 2-page fact sheet and some videos:

http://www.youtube.com/watch?v=tz1LaTO9P-8&feature=share&list=PLBEXDPatoWBlJU2U76iArz5U8SqvVj8_7&index=2

Title: Re: Mars EDL technologies
Post by: ClaytonBirchenough on 04/29/2014 09:48 PM
Armadillo used an inflatable decellerator on the STIG; it seems to have worked pretty well.

I'm having trouble finding any information on this... is there a PDF or anything floating around out there on Armadillo's inflatable decellerator?
Title: Re: Mars EDL technologies
Post by: rdiaz on 05/02/2014 02:51 AM
I'm wondering if there is anything more extensive on this. I'm only finding a 2-page fact sheet and some videos:


Starting at 15:10 http://www.nasa.gov/sites/default/files/ne0801_tdm-2_0.mp4 (http://www.nasa.gov/sites/default/files/ne0801_tdm-2_0.mp4).
Also, an older presentation by Mark Adler https://solarsystem.nasa.gov/docs/Adler_SIAD.pdf (https://solarsystem.nasa.gov/docs/Adler_SIAD.pdf).
Title: Re: Mars EDL technologies
Post by: rdiaz on 05/02/2014 02:59 AM
Armadillo used an inflatable decellerator on the STIG; it seems to have worked pretty well.

I'm having trouble finding any information on this... is there a PDF or anything floating around out there on Armadillo's inflatable decellerator?

Some images, commendable effort but I wouldn't say that it worked "pretty well"
http://highpowerrocketry.blogspot.com/2012/02/stiga-flight-2-to-95km-by-armadillo.html (http://highpowerrocketry.blogspot.com/2012/02/stiga-flight-2-to-95km-by-armadillo.html)
https://www.youtube.com/watch?v=Aw11NFz14sA (https://www.youtube.com/watch?v=Aw11NFz14sA)
Title: Re: Mars EDL technologies
Post by: Blackstar on 05/03/2014 07:24 PM
I think NASA has added a bit more to their website on this:

http://www.nasa.gov/offices/oct/game_changing_technology/game_changing_development/HIAD/index.html

Title: Re: Mars EDL technologies
Post by: catdlr on 05/16/2014 12:22 AM
NASA Briefing for Supersonic Saucer-Shaped Vehicle

May 15, 2014

A mission overview briefing about NASA's upcoming flight test of the Low-Density Supersonic Decelerator (LDSD) experiment will be provided to reporters attending a media day on Monday, June 2, at the U.S. Navy's Pacific Missile Range Facility (PMRF) on Kauai, Hawaii. The public can watch the briefing via live streaming, at 11 a.m. PDT (2 p.m. EDT/8 a.m. HST).

NASA's LDSD test is designed to investigate breakthrough technologies that will benefit landing future human and robotic Mars missions, as well as aid in safely returning large payloads to Earth. The NASA LDSD test over the Pacific Ocean will simulate the entry, descent and landing speeds a spacecraft would be exposed to when flying through the Martian atmosphere. During the test, a large saucer-shaped disk carrying an inflatable inner-tube-shaped decelerator and parachute system will be carried to an altitude of 120,000 feet (37 kilometers) by a giant balloon. After release from the balloon, rockets will lift the disk to 180,000 feet (55 kilometers) while reaching supersonic speeds. Traveling at 3.5 times the speed of sound, the saucer's decelerator will inflate, slowing the vehicle, and then a parachute will deploy to carry it to the ocean's surface.

Briefing participants will include:

-- Capt. Bruce Hay USN, commanding officer, Pacific Missile Range Facility, Kauai, Hawaii

-- Michael Gazarik, associate administrator of the Space Technology Mission Directorate, NASA Headquarters, Washington

-- Mark Adler, LDSD project manager, NASA's Jet Propulsion Laboratory, Pasadena, California

-- Ian Clark, LDSD principal investigator, JPL

The briefing will be streamed live on the agency's website at:

http://www.nasa.gov/nasatv

It will also be carried live on:

http://www.ustream.tv/nasajpl2

NASA has six potential dates for launch of the high-altitude balloon carrying the LDSD experiment: June 3, 5, 7, 9, 11 and 13. The launch window for each date extends from 7 a.m. to 8:30 a.m. HST.

NASA's LDSD carries several onboard cameras. It is expected that video of selected portions of the test, including the rocket-powered ascent, will be downlinked and streamed live to several NASA websites, including:

http://www.nasa.gov/nasatv

and

http://www.ustream.tv/nasajpl2

Decisions to attempt launch of the LDSD test will be made the day before each launch opportunity date. NASA will issue launch advisories via social media -- @NASA_Technology and @NASA - as well as the mission website and news media advisories.

For more information about NASA's LDSD, visit the mission page at:

http://go.usa.gov/kzZQ

NASA's LDSD program is part of the agency's Space Technology Mission Directorate, which is innovating, developing, testing and flying hardware for use in NASA's future missions. For more information about NASA's investment in space technology, visit:

http://www.nasa.gov/spacetech

Title: Re: Mars EDL technologies
Post by: RanulfC on 05/16/2014 01:04 PM
I am seriously begining to believe that NASA is going out of their way to "tweek" the UFO believers :)

Besides we ALL know THIS is what a real "Saucer-Shaped" reentry vehicle looks like:
http://www.military.com/Content/MoreContent/?file=PMsaucer
http://www.fantastic-plastic.com/LRVCatalogPage.htm

Randy
Title: Re: Mars EDL technologies
Post by: catdlr on 05/18/2014 05:29 AM
NASA June 2 Kauai Media Day for First Supersonic Saucer-Shaped Vehicle Test

http://www.nasa.gov/press/2014/may/nasa-june-2-kauai-media-day-for-first-supersonic-saucer-shaped-vehicle-test/

Quote
During the test a large saucer-shaped disk carrying an inflatable inner tube-shaped decelerator and parachute system will be carried to an altitude of 120,000 feet by a giant balloon. After release from the balloon, rockets will lift the disk to 180,000 feet while reaching supersonic speeds. Traveling at 3.5 times the speed of sound, the saucer's decelerator will inflate, slowing the vehicle down, and then a parachute will deploy to carry it to the ocean's surface.
Title: Re: Mars EDL technologies
Post by: AnalogMan on 05/22/2014 12:59 AM
NASA's Saucer-Shaped Craft Preps for Flight Test
May 16, 2014

NASA's Low-Density Supersonic Decelerator (LDSD) project, a rocket-powered, saucer-shaped test vehicle, has completed final assembly at the U.S. Navy's Pacific Missile Range Facility in Kauai, Hawaii.

This experimental flight test is designed to investigate breakthrough technologies that will benefit future Mars missions, including those involving human exploration. Three weeks of testing, simulations and rehearsals are planned before the first launch opportunity on the morning of June 3. LDSD was built at NASA's Jet Propulsion Laboratory, Pasadena, California, and shipped to Kauai for final assembly and preparations.

"Our Supersonic Flight Dynamics Test Vehicle number 1 arrived at the Navy's Pacific Missile Range Facility on April 17," said Mark Adler, project manager of the Low Density Supersonic Decelerator project from JPL. "Since then, we have been preparing it for flight. One of the last big assemblies occurred on April 30, when we mated the vehicle with its Star-48 booster rocket."

During the June experimental flight test, a balloon will carry the test vehicle from the Hawaii Navy facility to an altitude of about 120,000 feet. There, it will be dropped and its booster rocket will quickly kick in and carry it to 180,000 feet, accelerating to Mach 4. Once in the very rarified air high above the Pacific, the saucer will begin a series of automated tests of two breakthrough technologies.

In order to get larger payloads to Mars, and to pave the way for future human explorers, cutting-edge technologies like LDSD are critical. Among other applications, this new space technology will enable delivery of the supplies and materials needed for long-duration missions to the Red Planet.

The upper layers of Earth’s stratosphere are the most similar environment available to match the properties of the thin atmosphere of Mars. The Low Density Supersonic Decelerator mission developed this test method to ensure the best prospects for effective testing of the new and improved technologies here on Earth.

Anyone with Internet access will be able to watch live as video from the June test is relayed from the vehicle to the ground. The low-resolution images from the saucer are expected to show the vehicle dropping away from its high-altitude balloon mothership and then rocketing up to the very edge of the stratosphere. The test vehicle will then deploy an inflatable Kevlar tube around itself, called the Supersonic Inflatable Aerodynamic Decelerator (SIAD). After the SIAD inflates, the test vehicle will deploy a mammoth parachute called the Supersonic Disk Sail Parachute.

While people watching at home may be fascinated by how these two new technologies operate, the NASA flight team will actually be concentrating on a more fundamental question – "Will the test vehicle work as planned?"

"This first test is a true experimental flight test," said Ian Clark, the LDSD principal investigator from JPL. "Our goal is to get this first-of-its-kind test vehicle to operate correctly at very high speeds and very high altitudes. "

Although there is no guarantee that this first test will be successful, regardless of the outcome, the LDSD team expects to learn a great deal from the test. NASA has two more saucer-shaped test vehicles in the pipeline, with plans to test them from Hawaii in summer of 2015.

"We are pushing the envelope on what we know," said Clark. "We are accepting higher risk with these test flights than we would with a space mission, such as the Mars Science Laboratory. We will learn a great deal even if these tests, conducted here in Earth's atmosphere at relatively low cost, fail to meet some of the mission objectives."

As NASA plans increasingly ambitious robotic missions to Mars, laying the groundwork for even more complex human science expeditions to come, the spacecraft needed to land safely on the Red Planet's surface will become larger and heavier. This new technology will enable those important missions.

More information about LDSD is at: http://www.nasa.gov/mission_pages/tdm/ldsd/ (http://www.nasa.gov/mission_pages/tdm/ldsd/)

http://www.nasa.gov/jpl/ldsd/flight-test-20140516 (http://www.nasa.gov/jpl/ldsd/flight-test-20140516)

Photo Captions:

Top: Preparing for a Supersonic Test

A saucer-shaped test vehicle holding equipment for landing large payloads on Mars is shown in the Missile Assembly Building at the US Navy's Pacific Missile Range Facility in Kaua‘i, Hawaii.  The vehicle, part of the Low Density Supersonic Decelerator project, will test an inflatable decelerator and a parachute at high altitudes and speeds over the Pacific Missile Range this June.  A balloon will lift the vehicle to high altitudes, where a rocket will take it even higher to the top of the stratosphere at several times the speed of sound.

This image was taken during a "hang-angle" measurement, in which engineers set the vehicle's rocket motor to the appropriate angle for the high-altitude test. The nozzle and the lower half of the Star-48 solid rocket motor are the dark objects seen in the middle of the image below the saucer.

Middle: Hanging Saucer

In this picture, NASA’s saucer-shaped experimental flight vehicle is prepared for a Range Compatibility Test at the US Navy’s Pacific Missile Range Facility in Kaua‘i, Hawaii.  During the exercise, which occurred on April 23, 2014, all the radio frequencies interfaces between the vehicle, its balloon carrier and the missile range were checked. 

Bottom: Prepping the Parachute Deployment Device

An engineer works on the Parachute Deployment Device of the Low Density Supersonic Decelerator test vehicle in this image taken at the Missile Assembly Building at the US Navy's Pacific Missile Range Facility in Kaua‘i, Hawaii. From high altitudes above Earth, the vehicle will test two devices for landing future heavy payloads on Mars. One of the two devices is a mammoth parachute called the Supersonic Disk Sail Parachute.

That parachute will be released with the help of the Parachute Deployment Device, the can with barber-like stripes seen at the center of the picture. Inside is a 14.4-foot (4.4-meter) ballute, which is a cross between a balloon and a parachute. Once the test vehicle is at the right altitude, the ballute will be shot out of the can by a gunpowder mortar, after which the drag on the ballute is used to pull out the big parachute from a separate compartment.

All Images Credit: NASA/JPL-Caltech
Title: Re: Mars EDL technologies
Post by: AnalogMan on 05/22/2014 01:09 AM
Before the Drop: Engineers Ready Supersonic Decelerator
May 21, 2014

A saucer-shaped vehicle designed to test interplanetary landing devices hangs on a tower in preparation for launch at the U.S. Navy's Pacific Missile Range Facility in Kauai, Hawaii. The saucer, which is part of NASA's Low-Density Supersonic Decelerator (LDSD) project, will test two devices for landing heavy payloads on Mars: an inflatable tube and an enormous parachute.

The launch tower helps link the vehicle to a balloon; once the balloon floats up, the vehicle is released from the tower and the balloon carries it to high altitudes. The vehicle's rocket takes it to even higher altitudes, to the top of the stratosphere, where the supersonic test begins.

NASA has six potential dates for launch of the high-altitude balloon carrying the LDSD experiment: June 3, 5, 7, 9, 11 and 14. The launch window for each date extends from 7 to 8:30 a.m. HST (10 to 11:30 a.m. PDT and 1 to 2:30 p.m. EDT).

This image was taken during the vehicle's Integrated System Test, an operations rehearsal that engaged all of the teams and systems required for launch and flight, and ran through activities that will be conducted before and during launch, ascent, powered drop and flight.

http://www.nasa.gov/jpl/ldsd/supersonic-decelerator-20140521 (http://www.nasa.gov/jpl/ldsd/supersonic-decelerator-20140521)

Photo Caption:

The launch tower helps link the Low-Density Supersonic Decelerator test vehicle to a balloon; once the balloon floats up, the vehicle is released from the tower and the balloon carries it to high altitudes. The vehicle's rocket will take it to even higher altitudes, where the supersonic test begins.
Image Credit: NASA/JPL-Caltech
Title: Re: Mars EDL technologies
Post by: catdlr on 05/22/2014 01:54 AM
LDSD: We Brake for Mars: Part 2

 Published on May 21, 2014

In part 2, JPL engineer Mike Meacham explains how an inflatable decelerator will help larger spacecraft land on Mars. The device will be tested at the Pacific Missile Range Facility in Hawaii in June, 2014.


http://www.youtube.com/watch?v=G0asOKx5Xp0
Title: Re: Mars EDL technologies
Post by: Kaputnik on 05/22/2014 08:51 AM
What sort of g forces would a SIAD device produce? Seeing as they mention manned payloads...
Title: Re: Mars EDL technologies
Post by: AJA on 05/23/2014 08:44 PM
Why does the SIAD have to inflate post entry-interface as opposed to before? Would it allow more margin? (on increased area, or reduced pressure inside the inflatable shield, and therefore reduced mass) if the requirement to inflate after the onset of appreciable drag was dropped?
Title: Re: Mars EDL technologies
Post by: guru on 05/27/2014 01:46 PM
Why does the SIAD have to inflate post entry-interface as opposed to before? Would it allow more margin? (on increased area, or reduced pressure inside the inflatable shield, and therefore reduced mass) if the requirement to inflate after the onset of appreciable drag was dropped?

I believe peak g-loading on a traditional EDL sequence (somewhere between 12 and 16 g forces for the MSL for example) occurs prior to the time when the SIAD would be inflated.  Thus, with a greater surface area creating higher drag, if the SIAD were to be inflated prior to entry interface, the peak g-load, as well as the peak heating flux, could be even higher.
Title: Re: Mars EDL technologies
Post by: Jim on 05/27/2014 02:12 PM
Why does the SIAD have to inflate post entry-interface as opposed to before?

It isn't a heat shield.  It is a decelerator that can be used in higher velocity regimes than parachutes.
Title: Re: Mars EDL technologies
Post by: AnalogMan on 05/28/2014 11:20 PM
NASA’s Low-Density Supersonic Decelerator Tests New Deceleration Technologies
The Marshall Star - May 28, 2014

NASA’s Low-Density Supersonic Decelerator (LDSD) test is designed to investigate new deceleration technologies that could help land heavier payloads on planets like Mars. The test will take place at the U.S. Navy’s Pacific Missile Range Facility in Kauai, Hawaii, with the first potential launch date June 3.

Additional potential test dates include June 5, 7, 9, 11 and 14. The launch window for each date extends from noon - 1:30 p.m. CDT. Decisions to attempt launch of the LDSD test will be made the day before each launch opportunity date.

During the experimental flight test, a large balloon about the size of three football fields will carry the saucershaped test vehicle to an altitude of about 120,000 feet. It will then be dropped and its booster rocket will quickly kick in and propel it to 180,000 feet, reaching Mach 4. Once in the very thin air high above the Pacific, the first deceleration device, called a Supersonic Inflatable Aerodynamic Decelerator, -- the world’s largest -- will deploy, inflate and slow the vehicle.

A short time later the second deceleration device, a 30.5 meter parachute -- which is the world’s largest supersonic parachute and double the size of the one used on the recent Mars Science Laboratory mission -- will deploy and slow the vehicle further before landing in the ocean.

Current technology used for decelerating large payloads dates back to NASA’s Viking program from the ‘70s. In order to send humans and required equipment to Mars, new ways of slowing down heavy payloads through the atmosphere are critical.

Anyone with Internet access will be able to watch the test live as video is relayed from the vehicle to the ground. Websites providing coverage will include NASA TV (http://www.nasa.gov/nasatv) and via Ustream at http://www.ustream.tv/nasajpl2 (http://www.ustream.tv/nasajpl2). The LDSD Web page will also have daily updates on launch attempts, as well as the Twitter accounts @NASA_Technology (https://twitter.com/nasa_technology), @NASA (https://twitter.com/nasa) and @NASA_Marshall (https://twitter.com/nasa_marshall).

NASA’s Space Technology Mission Directorate in Washington funds the LDSD mission, a cooperative effort led by NASA’s Jet Propulsion Laboratory. NASA’s Marshall Space Flight Center manages LDSD within the Technology Demonstration Mission Program Office.

NASA’s Wallops Flight Facility is coordinating support with the Pacific Missile Range Facility and providing the balloon systems for the LDSD test.

http://www.nasa.gov/sites/default/files/files/star140528.pdf (http://www.nasa.gov/sites/default/files/files/star140528.pdf)
Title: Re: Mars EDL technologies
Post by: AJA on 05/29/2014 09:08 PM
Aah.. thanks guru, and Jim. I guess I read SIAD, but pictured HIAD. But since they've successfully tested IRVE, do they need to continue with SIAD? Or are they both part of the same project?


EDIT: Also, didn't Allen and Eggers show, from first principles, that the heating load is inversely proportional to the drag co-efficient? (http://en.wikipedia.org/wiki/Atmospheric_entry#Blunt_body_entry_vehicles) Which led to blunt body re-entries? Is that not applicable to such a decelerator for some reason? i.e. Increase the area, and thus the drag co-efficient, and ameliorate the heating problem?
Title: Re: Mars EDL technologies
Post by: catdlr on 05/29/2014 10:41 PM
May 29, 2014
MEDIA ADVISORY M14-097

NASA Sets Media Coverage for Saucer-Shaped Test Vehicle Flight in Hawaii

http://www.nasa.gov/press/2014/may/nasa-sets-media-coverage-for-saucer-shaped-test-vehicle-flight-in-hawaii/#.U4e2HPldWkE (http://www.nasa.gov/press/2014/may/nasa-sets-media-coverage-for-saucer-shaped-test-vehicle-flight-in-hawaii/#.U4e2HPldWkE)
Title: Re: Mars EDL technologies
Post by: catdlr on 05/30/2014 12:24 AM
NASA Coverage for Saucer-Shaped Test Vehicle Flight

http://www.jpl.nasa.gov/news/news.php?release=2014-168

Quote
On launch attempt days, journalists are invited to PMRF to watch the liftoff and flight of the balloon carrying the LDSD. June 3 is the first launch attempt day, with a launch window extending from 8 to 9:30 a.m. HST (11 to 12:30 PDT/2 to 3:30 EDT).

NASA's LDSD carries several onboard cameras. It is expected that video of selected portions, including the rocket-powered ascent, will be downlinked live and streamed live to NASA TV and online.

The public may watch the news conference on June 2, and the balloon launch and subsequent test on June 3, on NASA TV
Title: Re: Mars EDL technologies
Post by: Blackstar on 06/02/2014 08:03 PM
http://www.jpl.nasa.gov/news/news.php?release=2014-169&utm_source=iContact&utm_medium=email&utm_campaign=NASAJPL&utm_content=DailyBreakly20140602

NASA's 'Flying Saucer' Readies for First Test Flight
June 02, 2014

The first launch opportunity for the test vehicle is June 3, when the launch window opens at 8:30 a.m. Hawaii Standard Time (11:30 a.m. PDT/2:30 p.m. EDT). The test will be carried live on NASA TV and streamed on the Web. The Low Density Supersonic Decelerator (LDSD) will gather data about landing heavy payloads on Mars and other planetary surfaces.
Title: Re: Mars EDL technologies
Post by: catdlr on 06/02/2014 08:43 PM
Inflatable Heat Shields Could Drop-Ship Bigger Robots | Video

Published on Jun 2, 2014
The Hypersonic Inflatable Aerodynamic Decelerator, or HIAD, is rigorously tested in NASA's Armstrong Flight Research Center. This technology is being developed to deliver larger payloads to planets more efficiently.

https://www.youtube.com/watch?v=CWZAoKWd3fE
Title: Re: Mars EDL technologies
Post by: guru on 06/02/2014 09:44 PM
Aah.. thanks guru, and Jim. I guess I read SIAD, but pictured HIAD. But since they've successfully tested IRVE, do they need to continue with SIAD? Or are they both part of the same project?


EDIT: Also, didn't Allen and Eggers show, from first principles, that the heating load is inversely proportional to the drag co-efficient? (http://en.wikipedia.org/wiki/Atmospheric_entry#Blunt_body_entry_vehicles) Which led to blunt body re-entries? Is that not applicable to such a decelerator for some reason? i.e. Increase the area, and thus the drag co-efficient, and ameliorate the heating problem?

The drag coefficient is not synonymous with the drag.

Drag is equal to the product of the drag coefficient, the total dynamic pressure (which is directly proportional to air density and to the square of the velocity), and the facing surface area.

Doubling the diameter will double the Reynolds number, but this won't generally result in more than about a 10% change in the drag coefficient  - usually, that 10% is a decrease, unless you happen to just hit the sweet spot on the Re number axis, and at higher Reynolds numbers, the change in the drag coefficient vs the Reynolds number is essentially nil.  (Aerodynamics in the supersonic regime is in some ways simpler than in the subsonic one.)

But, doubling the diameter will quadruple the surface area.  So, assuming a constant mass, the vehicle endures four times the drag, meaning four times the deceleration, meaning as much as 4 times the rate of kinetic energy dissipation (that's the upper limit as decerlation time approaches infinity) over only 4 times the surface area, meaning that the heat flux either stays the same, or goes down.  In practice, over the time scale of a Mars EDL scenario, the heat flux is much closer to staying the same.  Add in the heat transfer effects caused by increased turbulence and a thinner thermal boundary layer, and one finds the possibility of a slight increase in total heat flux.  As you state, though, the heat flux will usually drop a small amount, so heat flux is not the issue I made it out to be.

In regards to peak g-forces, changes in density with altitude could give some advantage to a larger surface area earlier in the EDL process, meaning that with deceleration beginning higher up, one could spread out the deceleration some more, but how much it helps (if at all) depends on how much velocity is bled off prior to reaching the dense lower atmosphere.  If there is little velocity lost, than you wind up with nearly four times the g-forces at peak. If more than 75% of the velocity is bled off earlier, then the peak g-forces could go down.  For the cases considered, the increased area would still lead to much higher peak g-forces, but you can see that there are trade-offs and some optimization that goes into this.

More on the blunt body:  In a blunt body vehicle, the cushion of air helps keep the air flow in general, and the shock waves in particular, away from the vehicle.  Thus, a much larger portion of the dissipated kinetic energy (as much as 90%) gets carried away in the shock waves of a blunt body instead of being absorbed into the vehicle's hull, as would happen with sharper geometries.

As always, I am ready to be corrected if warranted.
Title: Re: Mars EDL technologies
Post by: bolun on 07/03/2014 01:35 PM
Dropship offers safe landings for Mars rovers

http://www.youtube.com/watch?v=nnIHWftmd0o

http://www.esa.int/spaceinvideos/Videos/2014/07/Dropship_offers_safe_landings_for_Mars_rovers

http://www.esa.int/Our_Activities/Technology/Dropship_offers_safe_landings_for_Mars_rovers
Title: Re: Mars EDL technologies
Post by: Blackstar on 07/11/2014 11:42 PM
That story has gotten badly reported--at least the headlines are misleading. They have led people to think that ESA is developing a helicopter for landing things on Mars when this was only a test device for Earth.
Title: Re: Mars EDL technologies
Post by: manboy on 10/09/2014 10:17 PM
Planned Flight of the Terrestrial HIAD Orbital Reentry (16 June 2014) (http://ntrs.nasa.gov/search.jsp?R=20140011452)


"The Terrestrial HIAD Orbital Reentry (THOR) is planned for flight in 2016 as a secondary payload on an Orbital Sciences Corporation (OSC) commercial resupply mission to the International Space Station (ISS). THOR will launch with its Hypersonic Inflatable Aerodynamic Decelerator (HIAD) stowed as a small cylinder between the second stage motor and the Antares launch vehicle fairing. Once the Cygnus cargo vehicle has separated from the second stage, THOR will likewise separate, autonomously re-orient itself, perform a de-orbit burn, then inflate the HIAD to a 3.7m diameter cone before atmospheric interface."

"Authority to Proceed with THOR is anticipated by the start of fiscal 2015."
Title: Re: Mars EDL technologies
Post by: guru on 10/18/2014 10:24 PM
NASA and SpaceX have released thermal video imaging of a night time supersonic retro-propulsive re-entry burn of a Falcon 9 rocket in Mars entry relevant conditions.

Watching it, I was amazed.  On the boost back burn, it was beautiful to see the entire ignition plume from a distance.  I also never really envisioned (although in hind sight I should have) the entire shock boundary layer being sloughed off.

The actual reentry burn itself looked rather more violent than I expected as well.  If you haven't seen it yet, enjoy.

http://aviationweek.com/space/thermal-images-spacex-falcon-9-rocket-descent

Original NASA press release:

http://www.nasa.gov/press/2014/october/new-commercial-rocket-descent-data-may-help-nasa-with-future-mars-landings/

Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/19/2014 12:50 AM
Interesting how much trouble we'll go through (conceptually) to avoid supersonic retropropulsion, how skeptical people are that it could possibly work.... Until someone simply bothers to test it.
Title: Re: Mars EDL technologies
Post by: sdsds on 10/19/2014 02:30 AM
Interesting how much trouble we'll go through (conceptually) to avoid supersonic retropropulsion, how skeptical people are that it could possibly work.... Until someone simply bothers to test it.

Yes I agree.

Except for the phrase, "simply bothers." You make it sound like this kind of testing was easy; like anyone with an afternoon to spare could have done it. I think that's underselling the boldness of SpaceX!
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/20/2014 11:00 PM
The first truly detailed Mars lander study (and the most detailed to date AFAIK) was the NA study of 1968.  They chose to go with supersonic retropropulsion after considering various options including ballutes.  They proposed a ballistic test program in the upper atmosphere. It's taken 46 years but we now know that the concept is sound.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/21/2014 01:24 AM
The first truly detailed Mars lander study (and the most detailed to date AFAIK) was the NA study of 1968.  They chose to go with supersonic retropropulsion after considering various options including ballutes.  They proposed a ballistic test program in the upper atmosphere. It's taken 46 years but we now know that the concept is sound.
Do you have a link? I don't see it here:
http://en.wikipedia.org/wiki/List_of_manned_Mars_mission_plans_in_the_20th_century
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/21/2014 01:56 AM
The first truly detailed Mars lander study (and the most detailed to date AFAIK) was the NA study of 1968.  They chose to go with supersonic retropropulsion after considering various options including ballutes.  They proposed a ballistic test program in the upper atmosphere. It's taken 46 years but we now know that the concept is sound.
Do you have a link? I don't see it here:
http://en.wikipedia.org/wiki/List_of_manned_Mars_mission_plans_in_the_20th_century

It was the lander that illustrates that article. :)

It was used in the Boeing IMIS (1968), the Von Braun Mars study (1969), the NASA Mars Expedition (1971) and a couple of others.

Not all of the source material is available, but if you search for "MEM" in the fora you should find the links to what is out there. If you can't I will upload them from home.

IMHO the design stands up very well, if we were to do a short stay Mars mission today we would still end up with something  like this.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/21/2014 03:31 AM
Thanks! I always am fascinate by Mars architectures, especially the older ones. Von Braun's Mars Project is my favorite for being fairly doable technically (except for scientific inaccuracies about Mars) and for using medium RLVs and vast amounts of on orbit refueling. It's the most ambitious on that list but I think it uses the least-powerful launch vehicle!
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/21/2014 09:22 AM
Were you able to download the relevant reports?
Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/22/2014 02:52 AM
Were you able to download the relevant reports?
yes. Looks like a capsule that lands on legs and has the center part launch as the ascent stage.
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/22/2014 03:01 AM
That's it, simple and efficient.
Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/22/2014 03:07 AM
That's it, simple and efficient.
Good approach, but I still think a reusable lander with ISRU is better, wouldn't have to be more massive.
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/22/2014 07:54 AM
That's it, simple and efficient.
Good approach, but I still think a reusable lander with ISRU is better, wouldn't have to be more massive.

Massing 49 tonnes at entry it is a bit larger than a original MD module, of which there were two, so 62% of the entry mass of a MD mission.

Two things to remember: 1)this is an opposition class mission, which almost never feature ISRU and 2), it is from 1968 when ISRU was not considered for an initial mission.  Given these limits, even  with the benefit of 46 years hindsight, it's hard to improve beyond a few tweaks.


Even with a conjunction mission if you don't want to do with ISRU you may end up with something like this to land the crew in and return them at the end.





Title: Re: Mars EDL technologies
Post by: Robotbeat on 10/22/2014 02:49 PM
Yeah, it's a good approach. Red Dragon-based sample-return would look basically identical but at a smaller scale.
Title: Re: Mars EDL technologies
Post by: Dalhousie on 10/22/2014 11:21 PM
Yeah, it's a good approach. Red Dragon-based sample-return would look basically identical but at a smaller scale.

Exactly. 
Title: Re: Mars EDL technologies
Post by: catdlr on 01/22/2015 12:11 AM
04 NASA Talk EDL cc

Published on Jan 21, 2015

https://www.youtube.com/watch?v=ZLBXnJ1JjVQ
Title: Re: Mars EDL technologies
Post by: catdlr on 05/08/2015 01:36 PM
must be some old film??  :o

NASA Low Density Supersonic Decelerator (LDSD)

Published on May 8, 2015
NASA's Wallops Flight Facility
NASA's LDSD test is designed to investigate breakthrough technologies that will benefit landing future robotic and human Mars missions, as well as aid in safely returning large payloads to Earth. The LDSD test over the Pacific Ocean simulates the supersonic entry and descent speeds a spacecraft would be exposed to when flying through the Martian atmosphere.

https://www.youtube.com/watch?v=wsELEJEtRI0
Title: Re: Mars EDL technologies
Post by: FishDaddyFlex on 04/08/2016 03:26 AM
Does anyone know if there are still plans for the 2016 LDSD test?  I cant find anything on it since the last test.  As I understand it, the parachute would not be able to be used even if successful unless funding was provided for another successful test (NASA needs two successful tests to deem it flight ready technology).  Maybe they have decided the parachute is just not going to be a reliable option without some sort of vastly new concepts or technologies.  I figured they would still test for the purpose of SIAD though.


EDIT:  I received some good responses to the same question in the LDSD thread:
http://forum.nasaspaceflight.com/index.php?topic=37724.msg1512879#msg1512879
Title: Re: Mars EDL technologies
Post by: savuporo on 05/03/2016 12:50 AM
Came across interesting dissertation for a control mechanism for large hypersonic deceleators.

https://vtechworks.lib.vt.edu/bitstream/handle/10919/50648/Atkins_BM_D_2014.pdf
http://arc.aiaa.org/doi/abs/10.2514/1.A32970

"Mars Precision Entry Guidance Using Internal Moving Mass Actuators"


The idea is not new:
http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1588605
Quote
We describe Sherpa — a S trap-on H igh-altitude E ntry R econnaissance & P recision A eromaneuver system that utilizes a moving mass system within an entry capsule to land a spacecraft precisely onto the surface of Mars.