Author Topic: MCT Speculation and Discussion Thread 4  (Read 502872 times)

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2560 on: 08/07/2016 08:26 PM »
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.

I don't disagree that it will be or already was considered; there are many possibilities that will be discarded as not optimum or unworkable.
Certainly no evidence that it will be used on Red Dragon, which would be the obvious opportunity to test it...
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT. None will be used on Red Dragon, which is not at all a reason to think it won't be used on MCT.

I don't have any particular belief that SpaceX will use something like HIAD. I don't envision they will. But you dismiss the possibility far too easily.
« Last Edit: 08/07/2016 08:27 PM by Robotbeat »
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Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #2561 on: 08/07/2016 10:40 PM »
The HIAD appears to be an unambiguous advancement on the static heatshield for landing arbitrary low-complexity payloads.  Funding for its development is sparse.  A few tens of millions thrown its way would establish some of the engineering as mature.

The problem is the same chicken-and-egg stuff as other human spaceflight engineering: We do not have a solid economic rationale to develop it yet.  Downmass requirements from the Space Station are tiny, and fully satisfied by most attempts at a reusable spacecraft.  New technology that shaves a few percent off of necessary upmass is not worth developing if it's only going to be used half a dozen times (and this is how far the planning forecast engages) and it is not guaranteed to work every time.  Absent economic rationale, it's a matter of the whimsy of whoever's funding advanced projects.

IRVE-3 -> IRVE-4 -> HEART -> routine use on Cygnus capsules... assuming funding and interest sustains, the papers suggest we could have completed this progression by now.  The roadmaps for this stuff portray it as not-very-far-out, but there are always "And then wait for more funding" points in the actual process.

I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;  from landing control precision to plume impingement to a question of orientation, a full working rocketship capable of taking off again is the last thing you would put behind such a drag device (still a possible net benefit, but less of one than any other return payload).  A gliding orientation with heatshields can fill a similar niche, particularly if there is a large degree of change in hypersonic aerodynamics using weight-shift or control-surfaces, between the capture/reentry and low-hypersonic regimes.  On top of that, as far as we can tell SpaceX has advanced the thermal capability of lightweight rigid heatshield design *considerably* during their tenure, though the specific progress is a trade secret.
« Last Edit: 08/07/2016 10:56 PM by Burninate »

Offline Torbjorn Larsson, OM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2562 on: 08/07/2016 10:59 PM »
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #2563 on: 08/07/2016 11:08 PM »
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?

It is unclear to me which or whether various bits of engineering (the fabric, the support, the air pressure) would limit the scale of a HIAD to a certain window or make it less mass-efficient than a rigid aeroshell at a given size.  I imagine some of the guys developing it could project various materials/mass limits out way beyond the planned development sizes that are testable on routine presentday launches, but I can't.

It was certainly investigated in part (if not in whole) because it might be used for manned missions to Mars.
« Last Edit: 08/07/2016 11:12 PM by Burninate »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2564 on: 08/08/2016 12:34 AM »
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?
HIAD is scalable to enormous sizes. It's not just for small scale EDL.
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2565 on: 08/08/2016 06:35 AM »
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Developed by NASA in that way? I only see them developing HIAD as a stage before using parachutes and parachutes limiting the downmass to Mars severely. Combining HIAD with SRP seems a serious headache.

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2566 on: 08/08/2016 09:25 AM »
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Developed by NASA in that way? I only see them developing HIAD as a stage before using parachutes and parachutes limiting the downmass to Mars severely. Combining HIAD with SRP seems a serious headache.

From http://gameon.nasa.gov/projects/hypersonic-inflatable-aerodynamic-decelerator-hiad-2/

The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) project is a disruptive technology that will accommodate the atmospheric entry of heavy payloads to planetary bodies such as Mars. HIAD overcomes size and weight limitations of current rigid systems by utilizing inflatable softgood materials that can be packed into a small volume and deployed to form a large aeroshell before atmospheric entry.

And from Langley's Game Changing Development Industry Day Presentation there is an interesting rendering of a Mars lander that combines a HIAD and retropropulsion. It even repacks the HIAD after landing.

http://www.nasa.gov/sites/default/files/atoms/files/gcd_industryday_hiad.pdf

« Last Edit: 08/08/2016 09:26 AM by OneSpeed »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2567 on: 08/08/2016 09:36 AM »
Yes, I am fully aware of that. But how much more than the 1t limit they have reached with Curiosity? No word on that in there. Will it support manned ERV MAV?
« Last Edit: 08/08/2016 09:37 AM by guckyfan »

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2568 on: 08/08/2016 10:13 AM »
Yes, I am fully aware of that. But how much more than the 1t limit they have reached with Curiosity? No word on that in there. Will it support manned ERV MAV?

If you were fully aware of it, then why did you 'only see them developing HIAD as a stage before using parachutes'? As Robotbeat suggested, HIAD scales to enormous sizes, certainly hundreds of tonnes. In other words 'heavy payloads'. If you examine the rendering closely, you will see that the lander has windows and a hatch. It is obviously intended to be manned crewed.
« Last Edit: 08/08/2016 09:33 PM by OneSpeed »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2569 on: 08/08/2016 12:31 PM »
NASA considers SRP to be used for EVERY Mars EDL concept big enough for humans.
It's now baselined. And HIAD is also used. There's no reason they can't both be used, and that is, in fact, NASA current preferred plan.
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Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2570 on: 08/08/2016 12:46 PM »
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2571 on: 08/08/2016 01:13 PM »
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.

Offline Torbjorn Larsson, OM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2572 on: 08/08/2016 11:29 PM »
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Ah, good to know! Extrapolating NASA's usually approach, they develop unique solutions for every mass scale to - ironically at high cost - fit their minimal budget. So now we have two scalable EDL techniques for Mars.

I would guess retrorockets is the far easier, cheaper method to scale tough. Just add engines as the craft diameter goes up. After all, that is how Flash Gordon did it! (Lots of engines looked good ...) And you need the engines for re-launch anyway.

Questions that popped up:

How far can NASA's current HIAD scale? Looks to me from artist conceptual sketches they want to re-engineer between prototypes for testing and their first use at, what, 10 m? What then if SpaceX needs a 15 m wide brake surface with tested technology?

Offline Torbjorn Larsson, OM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2573 on: 08/08/2016 11:40 PM »
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.

'It's bones, Jim, but now as we know it.' [Referring to the state of bodies of newly arrived martian colonists.]

Yes, I can't see a company invest in added mass and (fragile) complexity unless it is really necessary. By the way, wouldn't the side of a large craft offer a lot of negative lift? [Not an aerodynamist ... obviously.]

EDIT: Typo.
« Last Edit: 08/08/2016 11:42 PM by Torbjorn Larsson, OM »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2574 on: 08/09/2016 01:27 AM »
....
I would guess retrorockets is the far easier, cheaper method to scale tough.

As I said before:

HIAD and supersonic retropropulsion are complementary, not competing, technologies.
« Last Edit: 08/09/2016 01:28 AM by Robotbeat »
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Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2575 on: 08/09/2016 10:12 AM »
How far can NASA's current HIAD scale?

There are plenty of studies that consider HIADs up to 50m in diameter. They scale extremely well, and there is no reason they could not be made even larger.

It may be of interest that there are simulations of the phases of various MCT mission profiles in the L2 SpaceX Mars Discussion and Envisioning thread. Many of the simulations utilise HIADs of various sizes.

Offline Ionmars

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Re: MCT Speculation and Discussion Thread 4
« Reply #2576 on: 08/09/2016 11:59 AM »
..
...
...
Yes, I can't see a company invest in added mass and (fragile) complexity unless it is really necessary. By the way, wouldn't the side of a large craft offer a lot of negative lift? [Not an aerodynamist ... obviously.]
Perhaps the trade may include the mass of PICA-X running down one side of the vehicle versus the mass of HIAD to perform the same EDL.
* Mars' orbit: a convenient service station for an asteroid-sized spaceship en-route to Ceres. *

Online Oersted

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Re: MCT Speculation and Discussion Thread 4
« Reply #2577 on: 08/09/2016 04:07 PM »
A very thorough presentation of ideas for BFR/MCT from "coborop" at Reddit:
https://www.reddit.com/r/spacex/comments/4wks2h/fanmade_mct_and_bfr_architecture_cad_and_math/

Beautiful renders!:
https://imgur.com/a/2k10I

Online philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2578 on: 08/09/2016 05:10 PM »
A very thorough presentation of ideas for BFR/MCT from "coborop" at Reddit:
https://www.reddit.com/r/spacex/comments/4wks2h/fanmade_mct_and_bfr_architecture_cad_and_math/

Beautiful renders!:
https://imgur.com/a/2k10I

Interesting. Has the upper stage co-fire @ takeoff to increase T/W. Problem with Rvacs there.
What I like is someone not showing some BFR/BFS that is some ridiculous height like past Reddit posts I've seen elsewhere.  A >10m wide BFR gets very heavy quickly with propellant.  I'm confident that the reveal will be short and stout.
« Last Edit: 08/09/2016 05:11 PM by philw1776 »
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Offline DanielW

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Re: MCT Speculation and Discussion Thread 4
« Reply #2579 on: 08/09/2016 05:11 PM »
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.

Is there any benefit in using your engines as your "negative lift" component? Supersonic Perpendicular Propulsion SPP. Or do you get more deceleration from retro propulsion? How many G's of negative lift do you need to stay in the atmosphere?

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