Author Topic: Mars EDL technologies  (Read 109783 times)

Offline mmeijeri

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Mars EDL technologies
« 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.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #1 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.
« Last Edit: 08/16/2009 10:39 PM by mmeijeri »
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Online Kaputnik

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Re: Mars EDL technologies
« Reply #2 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.
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Offline mmeijeri

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Re: Mars EDL technologies
« Reply #3 on: 08/17/2009 08:20 PM »
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Offline Nathan

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Re: Mars EDL technologies
« Reply #4 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.)
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline simon-th

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Re: Mars EDL technologies
« Reply #5 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.

Offline simon-th

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Re: Mars EDL technologies
« Reply #6 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.

Offline Nathan

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Re: Mars EDL technologies
« Reply #7 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.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Nathan

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Re: Mars EDL technologies
« Reply #8 on: 08/23/2009 12:51 AM »
Actually probably only two aeroshells per falcon 9 heavy if given a departure c3 of 10kg2/m2.
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Offline Nathan

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Re: Mars EDL technologies
« Reply #9 on: 08/24/2009 09:04 AM »
Actually you're - we'd need more than that. Probably double each landing.
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Online savuporo

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Re: Mars EDL technologies
« Reply #10 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 ?
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Offline Nathan

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Re: Mars EDL technologies
« Reply #11 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.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline simon-th

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Re: Mars EDL technologies
« Reply #12 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).

Offline Nathan

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Re: Mars EDL technologies
« Reply #13 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.
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Offline simon-th

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Re: Mars EDL technologies
« Reply #14 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. 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 1300m at 66m packaging.

[/quote]

Offline Nathan

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Re: Mars EDL technologies
« Reply #15 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. 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 1300m at 66m 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.
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Offline simon-th

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Re: Mars EDL technologies
« Reply #16 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.

Online savuporo

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Re: Mars EDL technologies
« Reply #17 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.
« Last Edit: 08/25/2009 08:45 PM by savuporo »
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Online savuporo

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Re: Mars EDL technologies
« Reply #18 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 ?
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Online A_M_Swallow

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Re: Mars EDL technologies
« Reply #19 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.
« Last Edit: 08/25/2009 11:06 PM by A_M_Swallow »

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