Friday, November 22, 2013

Inspiration Mars straight talk

NASA will not have SLS or Orion ready by Jan. 2018.

Orion will not carry humans on board until 2021 at the earliest. Dragon is ready now. It does not need superdracos installed.

Bigelow modules are overkill. ILC Dover could provide Dragon with a 2000kg porch providing perhaps 50m3 of volume. Dragon mass is 4200kg.

A crew of two will require 4000kg (4m3) including themselves and consumables with no recycling assumed. Altogether that's 10200kg.

F9 can put 13000kg in LEO so more luxuries could be added. No SLS or FH required.

If you stop considering SLS & Orion you can use stuff that already exists so you can stop worrying about being able to meet the Jan. 2018 date.

A second launch is required. Either Atlas/Centaur or refueling the F9 upper stage. I have no idea what it costs to put a Centaur in orbit. The Centaur will do the job and exists. It would go into orbit first and then would have to mate to the Dragon.

The F9 upper stage would mate on the ground but the crew would have to wait in orbit for the refueling. We need to have experience refueling in orbit for future missions. We might as well put that milestone behind us now.

The TMI would happen before inflating the porch afterwhich cargo would be moved to provide plenty of space including some for privacy.

It doesn't cost a billion and it doesn't have danger of being delayed if they start now. Tito needs to forget SLS and Orion.

Update: NASA's response to Tito...
"Inspiration Mars' proposed schedule is a significant challenge due to life support systems, space radiation response, habitats, and the human psychology of being in a small spacecraft for over 500 days. The agency is willing to share technical and programmatic expertise with Inspiration Mars, but is unable to commit to sharing expenses with them."
Like I said.

Update: I'm curious to see what reaction this post gets?


Anonymous said...

There's a problem in using Centaur; the rocket needed to get a fully fueled Centaur into orbit. As currently used, Centaur is the upper stage, and part of its propulsive capacity is used to get to LEO.

What would be needed is a launch vehicle that can put a fully fueled Centaur in LEO. The mass of a fully fueled Centaur is a bit over about 23,000 kilograms. There is currently only one launch system operational that can loft that much to LEO - Delta IV heavy. In other words, you currently can't put a fully fueled Centaur in orbit without that LV, and you'd need some payload support structure engineering to make even that work.

You could offload a couple of thousand Kg in fuel and loft it on Ariane 5 or Proton (the two currently operational LVs with the largest LEO capacity, at around 21,000) but then your partially fueled Centaur comes up short on delta/v for the TMI, even before taking boiloff into account - hrmmm, though maybe not for the spacecraft mass you're thinking of. Math time!

In-orbit refueling of a F9 upper stage would be a viable option (and pretty much the only one if you're using F9 hardware), but if FH is available, use it to launch just its upper stage - you'd then have enough fuel remaining to dock the spacecraft to it and do the TMI burn.

Okay, your spacecraft mass is about half what my guess was. Let's go with your high-side estimate, 13,000 kg. What's needed for the TMI burn with that mass? What I'm wondering is whether launching a no-payload F9 would leave you enough fuel in the second stage to get the job done.

I apologize for the clumsy methodology I'm about to use, but I'm so rusty with math it's the only way I can think of, especially for partially fueled stages.

Okay, add the dry mass of the F9 upper stage (about 4500kg) to the spacecraft mass and you get 17500 kg. Figure fuel remaining as the payload capacity of F9 to Leo, about 13000 kg. It's actually be more than that, because vehicle launch mass would be less than normal, so lower gravity losses. Lower drag too, due to no payload fairing. So ballpark it at 15000kg fuel. That gives us an all-up spacecraft plus booster fuel mass of 32500kg. If we figure 350 ISP for Merlin D vac, that's 2.8kps delta/v. But what we need for TMI is 3.4. So, not even close. So... if we use F9 to loft a partially fueled Centaur, that knocks stage dry mass down by about 2000 kg, but it'd also bring us back to normal gravity losses, so 13000 kg fuel. Rune the same calc and we get (with the higher ISP of the Centuar's Lox/LH RL-10 making a huge difference) and we get 3.1 kps, still short.

Oh, and for comparison, if you use the same figures as for Centaur and drop the ISP down to that of Merlin, you get a delta/v of 2.4 instead of 3.1

Sooo... You either need in-orbit refueling of the F9 second stage, or a heavy lifer such as FH or Delta IV heavy, or you need a different concept for the TMI stage (Maybe make it two stages?) My guess as to the easiest (and most useful in knowledge gained) way; in orbit refueling.

BTW, Tito isn't proposing to use Orion. That'd blow his mass budget. He's proposing an "Orion-derived RV" that'd mass a lot less, and has the slight performance drawback of not existing, even as a design.

Totally agreed that waiting to use SLS and Orion will miss him his launch window, though I think the idea is awful for reasons going beyond that (Such as relying in a RV so altered that it's all new hardware, not an existing design at all).

Arizona CJ

ken_anthony said...

has the slight performance drawback of not existing

That is a priceless turn of phrase. I'm forced to steal it from you!

So to be clear. In orbit refueling of the F9 upper stage that was used to put the Dragon in orbit, assuming 13000kg (what about the mass of the upper stage as well?) would have the delta V to do the job?

Anonymous said...

How much fuel would remain in the stage after launching the Dragon? If you mean launching the Dragon plus crew and cargo for the mission, that'd mean a pretty much empty stage at LEO, so you're going to need more than the 13000kg fuel a second F9 could bring. Let me rerun the numbers and get a fuel figure for 3.4 kps... hrmm, about 30,000 kg. Ugh, two and a half F9 launches dedicated to fuel. doing a FH bare launch and using its upper stage would do the job with plenty of margin, so you could do the mission (maybe use a bit of the FH capacity for payload, too) with 1 F9 and 1 FH, or... 4 F9 launches. But, doing the in orbit refuel that way would be a mess; boil off would have to be dealt with, and that adds complexity and engineering.


ken_anthony said...

Good thing the FH is coming on line soon.

C J said...

ISP issues are a big issue here.

The 350 ISP figure I used for the Merlin Vac is a guess... I've seen figures all over the place.

Another way to do this, and perhaps a better way, would be to use staging for the TMI burn, so two or more burns.

Hrmmm... Or, there's another way that just occurred to me; reduce the delta/v needed for the TMI by about a third of a kilometer per second. Doing that might open up other booster options or configurations. I'm thinking lunar grav assist (Trans lunar injection takes about 3kps) and then a small burn at closest approach... about a hundred meters per second.

Basically, I'm thinking of roughly an Apollo lunar trajectory, but Apollo shots arrived ahead of the moon (relative it's orbital vector) but to do a grav assist you'd need to arrive just behind it. Hrmmm.. I wonder if the Draco thrusters could do 100 meters per second for a 13000 kg spacecraft? I'll crunch some numbers... 1200kg of fuel (but you can't use much of it... say 300kg) so 300kg. Let's run that through the rocket equation... I'll have to make a guess for Draco ISP, and given the fuel I'd say around 310. Rats, that only gives you 69 meters per second for a 13000kg stack. Plus, you'd lose the big booster (it's need to be jettisoned once spent, thus depriving you of a great radiation shield). Hrmmm... Let me think in this. I know you can't keep a F9 second stage and use it for a burn at the moon (boiloff losses) but maybe a small existing solid booster, such as a payload assist module, might be enough for the lunar burn.