It would seem that the big-rocket fallacy has claimed another victim. SLS is not the key to opening the solar system — it is a roadblock.
14 thoughts on “Inspiration Mars”
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It would seem that the big-rocket fallacy has claimed another victim. SLS is not the key to opening the solar system — it is a roadblock.
Comments are closed.
Shortly after the initial IM announcement, I was told by one of their principal people that Tito was a strong advocate of SLS.
Once again, we have otherwise good people ending up addicted to an unworkable symbol rather than something usable. Unfortunately, this creates bait for the pure pork advocates, and we can only hope it won’t be used to add to the damage they’re already doing to the work that really must be done.
His testimony was full of China-baiting and he failed to tell Congress what exactly it is he wants from them.
People live in bubbles. Whadayagonnado?
My guess is that Tito needed a free launch, and saw a chance to get it on SLS.
Could commercial have been the answer he needed? Probably yes, but I’ll bet that the reason it wasn’t is that he was coming up short of the needed funds. What commercial most glaringly lacks is a stage suited for the TMI burn for a large spacecraft, due to requirements for time in LEO to do a spacecraft systems checkout pre-burn (Ideally, at least a day. more like three). That causes boil-off issues for cryogenic fuels. There are at least two ways around that; launch something like Centuar (They’d need a stretched one) for on-orbit rendezvous after checkout, or go with a solid booster or two, maybe something adapted from an existing solid launch stage. So, it *could* be done commercially, but the financials would be a problem – it’d be costly. A “free” launch on SLS solves all the issues there rather nicely, assuming it actually happens in time. So I do see Tito having a motive here.
However, to paraphrase an old saying, “there ain’t no such thing as a free launch”. I think in following the lure of the free launch, Tito has killed any chance of Inspiration Mars actually flying. Worse, he’s reaffirmed the myth that to do things in space, you need government programs. And worse yet, he’s given SLS a shot in the arm.
If Tito chooses not to go with SpaceX… suppose Elon decides to do his own inspiration mar without any help? He’s got to test a lander on mars anyway?
I dunno where you get this impression of Elon from, but he’s not interested in small (human) Mars missions.
SpaceX would take some money to demonstrate an unmanned Dragon-derived vehicle landing on Mars, but when it comes to sending humans, Elon is a bigger big rocket buff than Dennis. If anything Musk thinks SLS is too small.
I agree (FXX 200mt) but he does have to test his landers. But again, you’re right, that doesn’t lead to a M1.1.
And Musk knows he’s got to make money doing otherwise useful things (and enabling other projects and customers) along the way, for his idea of reaching Mars…
SpaceX is the one company on the planet that has most of the hardware ready, or almost ready, to do an inspiration Mars style flyby. Assuming they have Falcon HEavy flying by then (if not, it’d still be possible with Falcon 9 1.1 multi-launch) most of what they lack is life support and a TMI stage.
They need about 2.1 mile per second delta/v from LEO to do this in the 2017 window. So, what’s the spacecraft mass? Dragon is about 5 tons. A Bigelow module or similar would be needed, though I have qualms; they’re goign to need to take along a LOT of supplies, and you can’t very well haul much during launch of an uninflated module. So, maybe the stretched Cignus isn’t a bad idea, otherwise you’ll need to repack in orbit. But, regardless of what they use, what’s a workable mass estimate for the all-up dragon plus whatever else? Hrmm, maybe two Dragons connected by some sort of inflatable or cylindrical tube? That’d at least give you redundancy for attitude control and re-entry. So, two dragons plus the connecting chamber, plus supplies… 20 tons total sound about right? Or am I too low?
Okay, so you’ve got 20 tons in Leo. That’s more than a Falcon 9 1.1 can lift (Which is about 15 tons, as I recall). So, FH, or 2 F9’s.
Now, you need a TMI stage or stages capable of boosting 20 tons by 2.1 mps. Bear with me here, I’m likely to screw the math up… A Centaur upper stage has 22,300 lbf of total thrust performance, if I’m reading that right. That’s accelerate 20 tons by… (ugh, I’m pathetically rusty at math) by… erk, I messed up somewhere. Okay, I’m so rusty that the only way I can think of to do this is add the dry mass of the TMI stage to the spacecraft mass, and use the fuel mass/ISP calculation to get feet per second.
A Centaur dry mass is about two and a half tons, so that brings Vehicle weight to 22.5 tons.
Centaur fuel load is about 23 tons.
ISP for the RL-10 engine is supposed to be 451.
Depending on how badly I bungled the math, that’d be a Delta/v of around 1.9 miles per second, a but slightly short of the 2.1 we need, and that’s for an on-orbit fully fueled Centuar, with no allowance for boil-off.
Given the mass of an all-up Centaur, it’d need FH to get it to orbit fully fueled. Hrmmm… it’d mean an ISP hit, plus a stage dry mass hit, but what about a FH launch with no payload, to get the second stage to LEO with as much fuel as possible? As a real rough rule of thumb, assume a fuel mass equivalent to payload capability. Using SpaceX’s figures of LEO payload of 116,845 lb, you should, as a guess, be able to loft a second stage into orbit with close to that mass remaining in fuel (no payload, no payload fairing, etc.).
That’s 58 tons of fuel. Even at the lower ISP of around 350, and a dry mass of 5 tons,
I’m figuring (unless I screwed up the first time) a delta/v capability for a 20 ton spacecraft of 2.45 miles per second, more than needed, so you have margins.
So, as a guess, they could do a Mars flyby mission using all SpaceX hardware (except life support) using two Dragons, a simple connecting module (storage/living space plus a docking port at each end… Not much different to building a fuel tank) and a Falcon Heavy upper stage for the TMI burn. It’d take either 2 F9 and 1 FH, or 2 FH, launches. If they do 2 FH, one launch for the crew, capsules, storage connector, supplies, etc. Do on-orbit docking and checkout, then send up the FH second stage for the TMI burn.
Yep, there are some big holes in the above scenario that go beyond my probably math goofs, but I don’t see anything that makes it impossible. The question is, would SpaceX want to spend the $$$? Plus, it’s a short timeframe (2017 launch window).
My personal guess; if they want to do this, they’d go for the 2019 (I think???) launch window that uses a Venus flyby as well, which is a slightly shorter flight duration plus gives you Venus as well as Mars, slightly lower Delta/v requirements, but higher reentry speed. (They can use aerocapture to mitigate some of that)
Dragon 5 tons, 2 tons (2m3) per person for 7 month trip (includes mass of person and consumables with no recycling assumed.) Bigelow modules are overkill. Have ILC Dover provide a 2 ton porch (perhaps 50m3 not inflated until after TMI) for the Dragon. That’s 11 tons for the 13 ton payload of the F9. Have a Centaur waiting in orbit providing more than enough delta V for TMI. Two launches the most expensive being the Atlas/Centaur. Fill the extra 2 tons with extra luxury supplies.
Once on their way, they inflate the porch and repack supplies so they have plenty of room to move around and some privacy.
You might not need the Centaur. Keep the upper stage and refuel it. I don’t have the numbers to know if that would work but they need to learn to refuel at some point anyway.
They could certainly accomplish this in 2017 with nothing new having to be developed. They certainly don’t need superdracos installed.
I recall a proposal from the days of Saturn-Apollo to do a Mars flyby using the upper stage of the Saturn V, refueled in orbit, as the TMI stage. The same might work with a Falcon 9 upper stage.
Confucius say “Man who ride Unicorn wind up with Very Sore Butt.”
Art Dula does have some surplus equipment that you could, with some work, dock a Dragon Cargo and a Dragon Rider onto either end and then do some remodeling and refurbish. It’s currently oxidizing on display strapped to a cart in a locked aircraft hangar stuck in a disused RAF airbase with a sign on the gate saying “Beware of The Leopard”.
Could probably buy it for the right price ….