Author Topic: Mars EDL technologies  (Read 105838 times)

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2717
  • Liked: 379
  • Likes Given: 342
Re: Mars EDL technologies
« Reply #20 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?
Waiting for joy and raptor

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8077
  • South coast of England
  • Liked: 247
  • Likes Given: 94
Re: Mars EDL technologies
« Reply #21 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.

Offline randomly

  • Full Member
  • ****
  • Posts: 511
  • Liked: 94
  • Likes Given: 39
Re: Mars EDL technologies
« Reply #22 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.

Online savuporo

  • Senior Member
  • *****
  • Posts: 4941
  • Liked: 857
  • Likes Given: 308
Re: Mars EDL technologies
« Reply #23 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.
Orion - the first and only manned not-too-deep-space craft

Offline simon-th

  • Full Member
  • ****
  • Posts: 952
  • Liked: 0
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #24 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.

Online savuporo

  • Senior Member
  • *****
  • Posts: 4941
  • Liked: 857
  • Likes Given: 308
Re: Mars EDL technologies
« Reply #25 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.
Orion - the first and only manned not-too-deep-space craft

Offline rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mars EDL technologies
« Reply #26 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.
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Offline Nathan

  • Member
  • Full Member
  • ****
  • Posts: 700
  • Sydney
  • Liked: 12
  • Likes Given: 2
Re: Mars EDL technologies
« Reply #27 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.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Nathan

  • Member
  • Full Member
  • ****
  • Posts: 700
  • Sydney
  • Liked: 12
  • Likes Given: 2
Re: Mars EDL technologies
« Reply #28 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.
Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Xentry

  • Full Member
  • *
  • Posts: 140
  • Lisbon, Portugal
  • Liked: 7
  • Likes Given: 4
Re: Mars EDL technologies
« Reply #29 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)

Offline simon-th

  • Full Member
  • ****
  • Posts: 952
  • Liked: 0
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #30 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.

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #31 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.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline Xentry

  • Full Member
  • *
  • Posts: 140
  • Lisbon, Portugal
  • Liked: 7
  • Likes Given: 4
Re: Mars EDL technologies
« Reply #32 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.   :(

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #33 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.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline simon-th

  • Full Member
  • ****
  • Posts: 952
  • Liked: 0
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #34 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.

Offline mmeijeri

  • Senior Member
  • *****
  • Posts: 7442
  • Martijn Meijering
  • NL
  • Liked: 70
  • Likes Given: 162
Re: Mars EDL technologies
« Reply #35 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.
We will be vic-toooooo-ri-ous!!!

Offline kraisee

  • Expert
  • Senior Member
  • *****
  • Posts: 10408
  • Liked: 237
  • Likes Given: 4
Re: Mars EDL technologies
« Reply #36 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.
« Last Edit: 09/02/2009 08:24 AM by kraisee »
"The meek shall inherit the Earth -- the rest of us will go to the stars"
-Robert A. Heinlein

Offline simon-th

  • Full Member
  • ****
  • Posts: 952
  • Liked: 0
  • Likes Given: 0
Re: Mars EDL technologies
« Reply #37 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.

Offline Michael Bloxham

  • Regular
  • Full Member
  • ****
  • Posts: 614
  • Auckland, New Zealand
    • Clean Slate Forums
  • Liked: 1
  • Likes Given: 6
Re: Mars EDL technologies
« Reply #38 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

« Last Edit: 09/02/2009 09:58 AM by Michael Bloxham »
Please help us to develop our high return-on-investment Humans-to-Mars architecture concept: http://forum.nasaspaceflight.com/index.php?topic=17360.msg636212#msg636212 Thanks!

Offline mmeijeri

  • Senior Member
  • *****
  • Posts: 7442
  • Martijn Meijering
  • NL
  • Liked: 70
  • Likes Given: 162
Re: Mars EDL technologies
« Reply #39 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.

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.
We will be vic-toooooo-ri-ous!!!

Tags: