Author Topic: MCT Speculation and Discussion Thread 3  (Read 255914 times)

Offline Lobo

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Re: MCT Speculation and Discussion Thread 3
« Reply #1060 on: 06/10/2015 07:04 PM »
I actually think the plan is probably to prepare the ground for MCT using stuff landed on a Dragon. Or at least was at one point.

Hmmmm...

I don't recall hearing that.  Also be interested to know what they could land in a Dragon that could actually feasibly clear an area sufficiently.
There's a lot of talk over on the Dragon speculation thread about what Dragon could land and deploy, but as Jim keeps coming back to, if they change Dragon too much, it's no longer a Dragon.  And Dragon's internal structure, hatch, etc isn't really set up to deploy a little robotic bulldozer or something that could move sufficient regolith and/or level an area for something like MCT.  It might be able to deploy something like iRobot or the quadruped Boston Dynamics robots, but I don't know what those things could actually excavate a landing area for MCT.

« Last Edit: 06/10/2015 09:30 PM by Lobo »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 3
« Reply #1061 on: 06/10/2015 09:44 PM »
I actually think the plan is probably to prepare the ground for MCT using stuff landed on a Dragon. Or at least was at one point.

Hmmmm...

I don't recall hearing that.  Also be interested to know what they could land in a Dragon that could actually feasibly clear an area sufficiently.

There was talk about Falcon Heavy having a role in preparation for MCT operation. We can speculate a lot about what this role could be. It could be placing com sats in Mars orbit. It could be sending rovers to Mars. If there are rovers to land it would be with Dragon or a Dragon derivate. They would not design new landers for that purpose, I am sure. The rovers would be designed with the abilities and limitations of Dragon in mind. They could survey the area to find out if it is suitable for the first landing e.g. finding water, finding a landing site and clearing it from smaller debris. Rovers for that purpose can be small but heavy.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #1062 on: 06/10/2015 09:57 PM »
As Jim said earlier somewhere, Dragon is too small to have a rover.  A larger rover could land via inflatable heat shield and parachute.  I think there my be just landers at various locations early on, to drill for core samples to see how much water is in various places to choose a colony landing site with the most water available for fuel manufacturing.  For landers and rovers, you will not really need a Dragon.  Larger rovers/landers might be brought to Mars via large SEP tugs.  A landing site for the colony and ease of landing MCT's is what must be found before MCT gets there.   

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1063 on: 06/11/2015 03:18 AM »
I think more focus needs to be placed on EDL, it is by far the 'long pole' around which everything else revolves, it is unfortunately MUCH more complex then the rocket equation type number crunching that we have mostly focused on.

The more I look at the EDL problem the more advantage I see from entry-from-orbit over direct-entry.  Virtually every aspect becomes easier by an order of magnitude, peak heat, total heat, g-forces you name it.  Viking landers entered from orbit and had the lowest TPS mass fractions (~2%) of anything that's ever entered Mars.  That's the kind of heat we need to be dealing with if we want a reusable vehicle without reapplying TPS materials which would FUNDAMENTALLY limit the vehicle to 1 payload per synod.

This means either propulsive capture at Mars or Airo-capture, but airo-capture would actually impose higher heat and g-forces then the following entry and landing meaning we would need to size systems for that and would give up much of the advantages gained.  Thus the best combination is a SEP transit vehicle delivering the lander to LMO followed by a mild entry, this maximizes reusability in BOTH vehicles.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #1064 on: 06/11/2015 03:26 AM »
Skipping entry is another option.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 3
« Reply #1065 on: 06/11/2015 05:02 AM »
Skipping entry is another option.

The NASA study for Inspiration Mars on Earth reentry concluded that PicaX works better with direct reentry. Not sure though it would be applicable to this situation.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1066 on: 06/11/2015 05:34 AM »
A skip could be inserted into either type of entry to further spread out the heat-loads, I'm not sure if it will change g-loads much and I think it requires that their be a high L/D.

On further thought, if the MCT is designed to handle low speed Mars-orbit Entry then it would have trouble with Earth Entry, even from LEO.  While the whole EDL process is easier on Earth because of the thicker atmosphere means your deceleration ends at low speed and high altitude such that a small parachute is all you need to land with, the actual thermal issues are greater then a Mars-orbital entry.  It would be awful wasteful to haul a thermal protection system all the way to Mars and back that your only going to use on entry to Earth. 

If we have SEP transit vehicles then we can avoid both direct entry to Mars atmosphere AND direct-return entry to Earths.  Ideally we would like to just leave MCT in LEO and reuse it from there, but this may not be operationally possible for reasons of maintenance or cargo-handling.   To avoid a wasteful over built TPS we need to reduce the Earth entry velocity to be comparable to Mars entry velocity, that's a difference of around 4 kms, which is just about the same DeltaV as we needed for Mars assent which is our tank size when a transit vehicle is available.

So I propose that we actually refuel the MCT in LEO (something we would already routinely do) for partially propulsive Earth Entry.  Rather then the usual brief burn to deflect trajectory into the upper atmosphere the MCT would almost completely empty it's tanks in a high altitude burn to drop it's velocity in Earth orbit from 7.5 kms to 3.5 kms at which point it would enter the upper atmosphere, as energy is proportional to velocity squared were looking at around an 80% drop in energy that needs to be dissipated by drag.  Naturally a bit of propellent is retained for the final touchdown but this would be much less then is needed on Mars because of the low terminal velocity in Earths atmosphere, and if necessary a parachute could be employed at this stage as it could be picked up in LEO along with the propellent.

With 3.5 kms as the maximum entry velocity the Thermal protection system could be something other then ablatives that have dominated in the past.  It would be a radiative and reusable material like the Shuttle tiles, but rather then fragile ceramics it should be METALLIC.  Basically it's a thin honeycomb of inconel over an alumina fiber baffle with titanium as the other side of the sandwich and it offers significant improvement in mass and durability over ceramics.  The lower the temperature it needs to resist the thinner it can be

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970005361.pdf
« Last Edit: 06/11/2015 05:46 AM by Impaler »

Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #1067 on: 06/11/2015 01:42 PM »
Could a large SEP tug, take a lander to Mars large enough to land a large metal pad that could unroll for the MCT to land on?  Maybe several landers in the same area with several rolls that could cover an area large enough for the MCT.  The landers could then be salvaged for building materials or habitats. 

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #1068 on: 06/11/2015 03:43 PM »
Zond did a skip. Zond is basically a Soyuz. So no, not much L/D is needed at all.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 3
« Reply #1069 on: 06/11/2015 04:05 PM »
Zond did a skip. Zond is basically a Soyuz. So no, not much L/D is needed at all.

Just hitting the atmosphere at a low angle. But not too low because it needs to bleed enough speed so it does not bump off to interplanetary space again.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 3
« Reply #1070 on: 06/11/2015 04:09 PM »
That's right. You need guidance. But this is not at all a showstopper for mass colonization flights (at which point you could spare a souled up MCT (one out of a thousand) to serve as a rescue craft in case someone does skip off into space or can't for whatever reason make entry.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Lobo

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Re: MCT Speculation and Discussion Thread 3
« Reply #1071 on: 06/11/2015 05:28 PM »
Here's an interesting bit on both aerocapture and direct entry from "Thompson Mars Cargo Entry".  (it can be found Googling that).

Quote
3.2 Direct Entry versus Aerocapture
Every Mars entry since Pathfinder has utilized a direct
entry, in which the entry vehicle performs EDL
without first going into orbit around the planet. This
results in entry velocities around 6 km/s, depending on
the Earth-Mars trajectory. This large entry velocity
results in significantly higher heat rates and heat loads
than entry from low Mars orbit; however, direct entry
has the benefit of not requiring extra heat shields, deployable decelerators, or propulsion for an insertion
maneuver, possibly resulting in lower mass and
complexity.
Direct entry with both a blunt body (L/D = 0.23) and a
slender lifting body (L/D = 1) were considered. Entry
mass was assumed to be 70 MT for both vehicles,
which is based on initial weights and sizing estimates.
The blunt body flew a trajectory that took it to Mach 5
at 10 km altitude. This altitude helps determine how
much time will be left for performing supersonic
deceleration. This can be thought of as a surrogate for
landed accuracy as with increased timeline more
maneuvers are possible to target the landing site.
On the other hand, the slender body has a tendency to
exit the atmosphere when the trajectory was flown liftup.
When flown at a constant bank angle of 85, the
slender body was able to stay in the atmosphere, but
due to its low hypersonic drag coefficient, the Mach 5
transition altitude is at 6 km, leaving little timeline
margin for the rest of deceleration. When bank angle
is set back to 0 once entry is assured, this transition
altitude can be increased; the downside to this class of
trajectory is that heat rates and heat loads are high
compared to other trajectories and vehicle
configurations.
Aerocapture involves entering the atmosphere from a
hyperbolic trajectory and using drag to slow the vehicle
down enough to exit the atmosphere in a closed orbit
around Mars. Previous studies have shown that
aerocapture can lead to a mass and cost savings over
other options including direct entry, aerobraking, and
propulsive insertion. Aerocapture reduces the kinetic
energy of the entry vehicle by 20-40% at entry
atmospheric interface. Entry from this slower velocity
reduces the severity of the heating environment
experienced by the vehicle, allowing for a thermal
protection system mass savings. This strategy also
allows the entry vehicle to reach Mach 5 at a higher
altitude compared to direct entry.
The performance advantages that aerocapture provides
must be weighed against the operational disadvantages.
With two entry sequences, any errors in orbit after the
aerocapture trajectory must be detected and corrected
to ensure that the entry sequence begins as planned.
The heat imparted to the heatshield on the aerocapture
pass also must be dealt with. Nested dual heatshields
have been proposed, in which the aerocapture
heatshield is jettisoned after the first pass through the
atmosphere with a second heatshield is used on entry
[15]. An alternative is the use of a hypersonic IAD
during aerocapture. The larger drag area decreases the
ballistic coefficient sufficiently that the vehicle
decelerates higher in the atmosphere, and sufficiently
reduces the heat rates seen on the vehicle. Overall,
aerocapture is a more complex mission mode than direct entry.
While these trade studies can be analyzed
for their performance at a conceptual level, more
detailed studies should be performed to identify the
most cost and mass efficient option.


So sounds like there's pro's and con's of both, and SpaceX will do trades I'm sure to determine which is best.
I would very much think that they'll look to a metallic system like I posted on up thread a bit, similar to what was looked at in alternative shuttle concepts, rather than than fragile ceramic tiles or an ablative shield. 
Perhaps there could be aerocapture, and then a certain time spent in orbit where heat load gained during the aerocapture could be rejected and the TPS system "cooled", and then an entry from Mars orbit.  A 2-phase process allowing for sufficient cooling in between that the TPS system doesn't need to be designed to withstand the full Direct Entry heatload?

And perhaps a similar method is employed on the return to Earth, for the same reason?

At the end of the day, I think you'll want to use the atmosphere's of those two planets to provide as much dV as possible without having to provide it with propulsion.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 3
« Reply #1072 on: 06/11/2015 08:45 PM »
If the MCT is to land back on earth, direct entry at Mars would probably be ok since the atmosphere is thinner and the heat wouldn't build up as much.  However, if the MCT just comes back to LEO then aerocapture might be used at earth to throw it back into LEO, but it still could land on Mars.  It could refuel in LEO, for reuse, but the cargo or people would still have to be ferried up somehow.  Two Falcon Heavies could bring up two 50 ton containers to offload into the MCT without the MCT landing back on earth.  This might be cheaper than landing and relaunching every MCT.  This could be done by use of a Tug with say three mechanical arms one to grab the MCT and the Falcon Heavy, and one to transfer the cargo pods.  This would be like the Dragon is grabbed by the mechanical arm on the ISS to assist in docking. 

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1073 on: 06/11/2015 09:14 PM »
From what I've read a radiative cooling system (which is what the shuttle used and what the metallic systems would be) are limited in their heat FLUX capacity, but generally are able to endure for a long time.

This would make them a poor match with an airo-capture maneuver as they would experience brief pulses of very high intensity heat flux.  Also the whole system would need to be engineered to meet the high heat of the first pass which from my understanding is only mildly lower then the heat flux of direct entry at the same speed.

Now Airo-braking (many very high altitude very gentle passes to lower periapsis) would be more compatible but this requires that your initial entry velocity is only just above capture which means it needs to be proceeded by propulsion.

Using propulsion to capture and circularize down to LMO looks to me to be the only way to truly have a light weight and fully reusable TPS.  Interacting with the atmosphere while still at high speed just gives all kinds of trouble and when we have high ISP propulsion available in the form of SEP the cost in propellent mass should be far far less then the TPS needs which are converted into PURE PAYLOAD for the lander.

Viking probes experienced only 21 W/cm^2, I don't know what the peak temperature was or would be when you look at the different ballistic coefficients and L/D ratios, and peak temperature that is what primarily determines the mass of a metallic TPS.
« Last Edit: 06/12/2015 12:58 AM by Impaler »

Offline Burninate

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Re: MCT Speculation and Discussion Thread 3
« Reply #1074 on: 06/11/2015 11:08 PM »
From what I've read a radiative cooling system (which is what the shuttle used and what the metallic systems would be) are limited in their heat FLUX capacity, but generally are able to endure for a long time.

This would make them a poor match with an airo-capture maneuver as they would experience brief pulses of very high intensity heat flux.  Also the whole system would need to be engineered to meet the high heat of the first pass which from my understanding is only mildly lower then the heat flux of direct entry at the same speed.

Now Airo-braking (many very high altitude very gentle passes to lower periapsis would be more compatible but this requires that your initial entry velocity is only just above capture which means it needs to be proceeded by propulsion.

Using propulsion to capture and circularize down to LMO looks to me to be the only way to truly have a light weight and fully reusable TPS.  Interacting with the atmosphere while still at high speed just gives all kinds of trouble and when we have high ISP propulsion available in the form of SEP the cost in propellent mass should be far far less then the TPS needs which are converted into PURE PAYLOAD for the lander.
Low TRL, but how about MAC?

The aeroshell and the HIAD are highly reliant on the shape and mass distribution of the vehicle, but not so with a magnetoshell attached to the spacecraft with cables.  In fact, you can use it as a drogue to control orientation as you extend those cables selectively.
« Last Edit: 06/11/2015 11:35 PM by Burninate »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1075 on: 06/12/2015 01:17 AM »
You got me, that would be a way to do airo-capture (and subsequent airo-braking at a much faster rate) without much heating, BUT you would still experience high G-forces which means less savings on structural mass, though on the other hand the fact the device is dragged behind you means your experiencing tensile forces which might be easier to handle then the typical compressive forces on an entry vehicle.

Arguably the Metalic TPS is the option to go with because of it's much higher TRL, my understanding is that it's basically already been done as part of the X-33 development, in fact it seems to be one of the few parts of the design that weren't giving anyone a headache.  http://www.nasa.gov/centers/ames/news/releases/1999/99_09AR.html  And remember this is a system considered capable of Earth entry velocity, we would be DOWN GRADING this material to accommodate a Mars entry which would be done by making the insulation thinner and or using a less 'super' alloy in the skin like mere titanium rather then inconel.

Magneto assisted capture can thus be viewed as a means of increasing the efficiency of the SEP transit vehicle, allowing it to do the last leg of it's mission (delivering the lander to LMO) using less propellents.  Attaching it to the transit vehicle also avoids any complication in how to attach it to the lander and reel it back in during decent.

Offline Sohl

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Re: MCT Speculation and Discussion Thread 3
« Reply #1076 on: 06/12/2015 02:48 PM »
Could a large SEP tug, take a lander to Mars large enough to land a large metal pad that could unroll for the MCT to land on?  Maybe several landers in the same area with several rolls that could cover an area large enough for the MCT.  The landers could then be salvaged for building materials or habitats.

Pad-X- is back, baby!   :o

"These pads are heavy... heavy METAL!"   8)   A most Excellent Adventure.

Edit: improved Bill and Ted pop ref accuracy.
« Last Edit: 06/12/2015 03:05 PM by Sohl »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1077 on: 06/12/2015 04:08 PM »
Why not simply roll the pads up and tuck them under the MCT itself near but clear of the engine nozzle .  If were looking at a Biconic shape then the bottom of the vehicle is not exposed to reentry and their is plenty of empty space necessitated by the length of landing gear and the engine bells (remember they are vacuum optimized so BIG, like F-1 big.

With one end attached to the vehicle undercarriage, and a rest wrapped around a bar held in place by a pin you simply drop to roll to the ground, kick it to unroll it under the bell nozzle and then detach and pin it down with some stakes.  Very simply manual task that an Astronaut will only need a few minutes for, no automated deployment is needed because while craft may land without anyone present, they won't take off again until people have landed and done proper inspections anyways.

This would be adequate for the first few landers, each deploying the debris mitigating mesh rolls under itself once landed (Im assuming small vernier jets for landing on unmodified ground) so that it may take off safely.  Once a few meshes are deployed in this way AND we have demonstrated pin-point landing ability the mesh can be detached and combined together into a landing pad, presumably at a spot where the ground has been leveled and compacted too.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 3
« Reply #1078 on: 06/12/2015 09:24 PM »

Arguably the Metalic TPS is the option to go with because of it's much higher TRL, my understanding is that it's basically already been done as part of the X-33 development, in fact it seems to be one of the few parts of the design that weren't giving anyone a headache.  http://www.nasa.gov/centers/ames/news/releases/1999/99_09AR.html  And remember this is a system considered capable of Earth entry velocity, we would be DOWN GRADING this material to accommodate a Mars entry which would be done by making the insulation thinner and or using a less 'super' alloy in the skin like mere titanium rather then inconel.


Additionally, this report is from 16 years ago.  Materials/metallurgy has come a long way since even then.

There may even be better materials available (or could be made soon available) today.

There could be materials adequate for the job of direct entry at Mars and Earth from interplanetary speeds.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 3
« Reply #1079 on: 06/13/2015 12:33 AM »
Metallurgy has not changed THAT much, the most advanced nickel based SUPER alloys were being employed on the X-33 and they still needed to use Carbon-Carbon on the nose cone and leading edges because no metal would handle that heat for a vehicle intended just for LEO reentry. 

A lot of diminishing return can be seen in development of these alloys.  The original nickel super alloy was discovered in 1929 as a mere curiosity before the jet age made it useful, development continues but a whole 'generation' of advancement using incredibly exotic additives claws us only 50C higher melting points now.

No way can they do anything more then a LEO return, the speed of direct entry from lunar return is 11 km/s, return from Mars would be similar.  That's going to be way more energy and way higher heating rates which are proportional to velocity CUBED from what I've read.  And even if they could you would be looking at higher mass in insulation behind the outer-skin to prevent the vehicle from completely melting AFTER landing as the skin heat soaks into the frame.  The shuttle upon landing had to be connected to water coolant circulated under the skin to keep it from melting.

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