Tuesday, June 18, 2013

Orion Service Module Overweight

Problem. Solution: Sundancer.


Arizona CJ said...

Hrmmm... I've been mumbling for years that Orion's all-up mass would be significantly more than claimed.

My guess; they trim both weight and capability from the SM, and maybe Orion as well.

For a return from the moon or an interplanetary return, I think Orion makes zero sense; it means hauling a hell of a lot of mass along, mass that's only needed for the final minutes of the voyage. Actually, I can't think of a mission where Orion does make any sense. Given the Orion's mass, you could send two Dragons, or better yet, a Dragon and a module.

Sundancer and Orion mass about the same, and Sundancer can't be used as an Earth return vehicle without a lot of Delta V to get it to LEO - or can it? Could a Sundancer (or similar) aerobrake into LEO via multiple passes? Once in LEO, they could dock with a reentry vehicle such as Dragon for the trip down.

I do know that aerobraking can be used on a spacecraft without a heatsheild - it's been done before. (Three times for Mars orbiters, I think.).

ken_anthony said...

It couldn't hurt to find out.

ken_anthony said...

Sundancer and Orion mass about the same

Sundancer has a slight edge in mass, but it's the internal volume that pushes it over the goal line. But as you said, a Dragon with an inflatable module may be a better way to go.

Then again, that may be the whole point of the MCT. Elon has looked at the issues from both a business and customer sense. I have great anticipation for the unveiling.

Volume is going to be very important for trips that take months.

Arizona CJ said...

Ken, I totally agree regarding volume being critical.

Personally, I think being cooped up with several people in an Orion would be (for me anyway) impossible to endure (I can't even stand city life - that's why I live away from cities or towns). That's why I'd never volunteer for Mars One, one way or not; the amount of living space per person would be very limited on the surface or in space. Way too crowded for me. But, that's just me. For those who are willing and capable and want to go, I support them.

I do however think that having more volume per person than Orion could provide is essential for anything beyond the Moon.

As for Aerobraking into Leo being possible for a Sundancer... it depends on materials used in the outer skin. If they can take 400F, then no problem. If they can take 350F, then maybe. What limited temp data I've been able to find for repeat aerobraking into orbit is for Mars and Venus, and seems to be around 375 F for short periods.

For comparison, tinfoil would be more than adequate by a factor of nearly 3; it's good to about 1100F (and melts at about 1200F)

How much Delta-V would be needed to get into an aerobraking orbit? I'm too lazy to do the math, but for a rule of thumb we can use Inspiration Mars' incoming velocity would of about 8 miles per second (What they called aerobraking as an option they considered was actually airocapture into an aerobraking orbit)

Earth escape velocity is about 6.95 miles per second. So, orbital velocity at perigee for a very elliptical orbit (one with an apogee well beyond the moon)would be a bit less than that, say 6.6 miles per second at a 100 mile perigee as a guess. So, to get a sundancer or similar into such a highly elliptical aerobraking orbit, and using Inspiration Mars' velocity at atmospheric interface of 8 miles per second,reduced to seven by a lunar gravity assist, you'd need about a mile and a half per second delta-v for capture - And I'm betting such a propulsive ability would weigh one hell of a lot less than lugging along an RV.

Hrmmm... I'll bet a Sundancer (assuming its solar panels can retract) could be equipped with a ballute; an inflatable heat shield. Then it could do aerocapture instead of aerobraking, and need no delta-V except for a very small amount to raise the perigee after apogee is at LEO. I'm thinking of aerocapture into an aerobraking orbit, not aerocapture all the way to LEO insertion (which would put a lot more G and heat on the spacecraft).

If that could be done (either some deltaV for aerobraking, or a ballute for aerocapture) then Sundancer or similar might well be the best option for an asteroid mission, a Mars return mission, long duration Lunar, etc.

ken_anthony said...

Mars one talks about (notice the mounds behind their line of Dragons) more space for the colonists. But I think their mental picture doesn't include people building it because it belongs to them where they'd be naturally inclined to improve the value of their property. Mars One colonists are employees making them basically bond servants.

An inflatable ballute is exactly what I was thinking. Light weight and small volume when not in use. You don't have to look very far for a vaccuum do deflate it. They might even keep a spare handy.

Could they just use the dragon heat shield (the wider Mars One Dragon) and some strategically placed sheathing on the Sundancer? The Dragon would be attached and protect the forward airlock. Perhaps the forward section of the Sundancer could have a very thin coating of PicaX?

Arizona CJ said...

My guess is a ballute would weigh less than a Dragon heat shield. A heat shield needs to block heat, while a ballute skin just needs to be able to withstand it (the space between its outer surface and the hull provides the needed insulation)

A big advantage with a ballute for aerocapture is the increased surface area Vs. a heat sheild means you're doing your braking higher in the atmosphere, so you have a much lower heat load.

Here's a PDF I think you'll find interesting.


That's focused on using ballutes for reentry from ther moon, which would entail a higher heat load than aerocapture due to the huge difference in delta-v involved. (about 7 miles per second vs. less than two)

That PDF gets into materials, which got me thinking... the Sundancer (or any other inflatable) already has many similarities to a deployed ballute, so maybe a lot of complexity and mass could be saved by simply using a suitable material for the outer skin, and making the solar panels retractable?

For Mars One living space, the colonists would still need materials to build those earthberm habs, so how much living space per petson would be feasible? At best, maybe the size of a small hotel room or small apartment? That would probably be fine for many, but I know I could never cope long term. I built myself a 4000 sq ft. home and need every bit of it - and I live alone. I found 2000 sq ft to be very cramped. (but I'm strange in that regard - most humans are quite comfortable with city living and its crowding, but I couldn't cope with it).

On the other hand, it'd be comfortably far from any cities. :)

ken_anthony said...

This link?

My basic habitat design is a ten meter wide and deep ditch 50 meters long. This is room for two floors and fits inside your average half acre plot (40m x 50m actually) with plenty of room to spare for adding more later. In other words, 2.5 times your 4000 sq. ft. home. They could go smaller, but I'm with you, I think they should all have mansions because they can. Most of their lives should be spent in a shirtsleeve environment, including a garden (at 10 psi) with a view sitting on top of their home with direct access.

They will definitely need a tractor or more. One lander could provide them with parts for two that they could assemble in a few days.

That pdf is interesting. A bit different from what I wrote about.

Arizona CJ said...

I just read your linked article (I somehow missed it when posted.) Excellent! (and thanks for the hat tip for the PDF link, too!).

The trench-and-cover concept sounds good, but how do you make it airtight? Even if you make brick or cement ISRU, that's not airtight. Maybe cover the interior with a plastic membrane? Or some local materials... maybe iron?

10 PSI? Hrmmm... Can humans survive long-term at 10 PSI? I'd hazard a guess that the answer is yes, as that's about the pressure at my house (7000 feet, so it's usually around 10.8 PSI). The high altitude does cause issues with everything from cooking to tire pressure to computer and appliance cooling, but it's not that big a deal once you understand it and the things needed to cope (such as extra cooling fans for computers and the hot coils on refrigerators). It also gave me a good laugh when I went to Machu Picchu (7900 feet) and was staying in a guest house at about 6500 feet, where they kept warning me, over and over, about the perils of high altitude. :)

IMHO farms would be needed for far more than food and O2; one of the most essential things they'll need to make is plastics, and making the hydrocarbons organically might well be the easiest way.

I'm not a fan of relying on solar power for a colony. Between the reduced sunlight, month long dust storms, and radiation shortening the life of the arrays, I think they'd need nuclear power (which would also be a needed heat source, not just for living but for certain chemical reactions). The upmass would probably be less than the solar arrays and the massive batteries they'd need to cope with dust storms that can block the sun for a month or more. A nuke would also facilitate placing the colony in the high northern latitudes at the ice cap edge, where water would not be in short supply.

ken_anthony said...

You're welcome.

That's funny since I live at about 10 psi here in Springerville AZ.

I was thinking very thin plastic because the structure itself provides the strength to support it, but some spray on coating should be sufficient. Zubrin says just spray water, but I'm not happy with the idea of igloo living.

Compress earth (mars) brick would provide solid walls between rooms after the trench is dug. They could make each room airtight without having to maintain full life support when they don't need all the extra space and save on some energy that way. They might do water spray in some rooms as a temporary solution until they are ready for a more permanent solution. I don't see making things airtight as a very difficult problem. They'll figure out the best construction practices by experience.

It's hard to get a good pizza at 10 psi, but we survive.

I agree about farms. The important thing is they will be able to make plastics.

It certainly makes sense to have nuclear, but the point is solar is not a show stopper and people forget that if you have power you can make fuel for generators as well with nickel hydride batteries for backup (which are simple, almost indestructible and last forever.)

I think even in a dust storm, solar would allow them to make enough fuel for generators. But definitely they should build thorium reactors.

Arizona CJ said...

The real show-stopper for Mars habitability could be related to gravity and pressure; is it possible to make a good cappucino at 10PSI and 1/3 G? Foaming the milk is hard enough just at 10PSI, but what about 1/3 G?

I'm not far from Prescott, and I liked the Springerville area. I almost moved to the area a few years ago (I was eying some land outside of Nutrioso) but then I found my present home. It's much less of a hassle to get to Phoenix Sky Harbor from here so this has worked pretty well.

On the Sundancer aerobraking issue, I've been wondering; is it worth the fuel (or aerobraking mass) to get to LEO from Mars to dock with an RV? If you're not reusing the sundancer, why not use an ultralight RV that you take along? I'm thinking something like MOOSE, which would mass about 200 pounds (the figures were around 400, but that includes the astronaut and his space suit) and be the size of a large suitcase (and that's with 1950's tech).


They could stow externally on the sundancer, and make good rad shielding.

I've never understood why something like this isn't used on ISS for "lifeboat" purposes; far longer shelf life than Soyuz, and is individual, so a lone crewman could be evaced in case of need without taking away the Soyuz. It also has the advantage of not needing a docking port. It'd be even better with a PicaX heatsheild instead of the denser, heavier ablative envisioned for it, and with such a sheild could do a direct entry from a Mars-Earth transfer orbit. And it'd be very cheap to build.

ken_anthony said...

It's too simple for a bureaucrat to wrap their heads around. It doesn't build turf.

Arizona CJ said...

I think I've solved the dilemma over what to line the trenched and backfilled Martian habitats with to keep the air in; hides. The hides of bureaucrats.

If Mars One would do that, I'll bet they'd have no shortage of donations.

ken_anthony said...

Now you're on to something. Skin is air tight after all.

I can think of a lot of government employees that could use a good tanning!

Arizona CJ said...

It'd also be a historic first; they'd be doing something that's actually useful. :)