sevenperforce
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Posts posted by sevenperforce
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I'd have to dig a little to be sure, but I'd guess that the dry mass of the solid booster core is so low, comparatively, that it's still quite fine.
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1 hour ago, tater said:
Yeah, that's my real point. We already agreed that 3 years was absurd, but even 8 is absurd. I think in 8 you might be able to get to the point of having defined the hardware to the point you could consider testing it. Unmanned in the case of any landing hardware, and perhaps manned in LEO for a transfer vehicle. That's with Apollo-like effort.
Given plausible lifters in that timeframe, I think that you'd dump aerocapture, and just bite the bullet and bring the extra propellant and pay homage to the god of the rocket equation.
There is a reason 2033 is often cited---there are opposition launch opportunities for ~1 year round trips with 30 days on the surface, and some have reentry velocities around 15km/s. Most other opposition windows put the Earth entry at closer to 20km/s. I think heat shield tech need to be tested in that regime, I'm also unsure of the g-loading calculations for the crew. Opposition missions minimize the life support issues, and might even allow for more redundancy in that area (spares, etc). With the current DRA, the MAV is sent ahead anyway, and that craft can do a direct martian entry I would assume. The descent vehicle would be able to be far lighter then, and dragging along the extra ~2km/s to insert to martian orbit might not be as insane.
Aerocapture of the manned landing vehicle itself seems pretty doable. EDL on Mars requires heat shield and propulsion as a matter of course, so if you can manage direct entry and propulsive landing, you should also be able to manage aerocapture and circularization.
Then, as I outlined previously, you can take advantage of propellant transfer (assuming you solved this problem before, in order to refuel your vehicles for TMI) to beat the rocket equation. Using aerocapture to get your return prop into Martian orbit, then transferring it back to the tanks of the bus you used to insert the transfer hab while you execute your EDL, seems very advantageous.
And this allows partial or total reuse, which is nice if you can do it for cheaper than the alternative.
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2 hours ago, shynung said:
NASA Mars Reconnaissance Orbiter mission used an aerocapture maneuver. This reduced the fuel needed for Mars orbit insertion by half.
As I understand it, the MRO used its engines for the initial insertion, establishing an elliptic Mars orbit, then adjusted its periapse to gradually trim off orbital energy one orbit at a time to adjust. It was excellent for the mission requirements, of course, but it's very different from a much more aggressive "true aerocapture" where a single pass through the atmosphere moves you from a hyperbolic orbit to an elliptic one. MRO needed no special heat shield, while a true aerocapture requires a heat shield and high-gee resistance.
2 hours ago, tater said:Even with a JFK-style time limit that was being pushed hard, I don't see 2024 as plausible. I think this is why Mars is always so far off, and continues to be. It would need real funding for the clock to start ticking, since that doesn't happen, it's always in the vague future.
Think about 2024. You'd need to launch some hardware in 2020. Not an experiment, like Red Dragon, actual mission, flight article hardware, but unmanned. If there is an issue, then you address it, and refly the next window, and only if that works do you send people. At some point, before 2024, you look at your mission duration, and you fly the transfer vehicle to LEO, and test the life support. Heck, you might send the actual vehicle up, and put people aboard for 3 years, but that means sending it up by 2021. After testing, assuming it's good to go, you attach the stages for Mars (an Earth departure stage, a Mars insertion stage, and a return stage), then go.
A free return seems like the only remotely possible goal that could be achieved in something like a 10 year window with real effort to me, largely because the spacecraft testing could be done entirely in Earth orbit. You could even test a stage, and send it to cislunar space for a while.
A Martian sample return could be launched in 2020, if enough money was poured into it.
But right now we don't even have a hab that could make the journey manned.
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19 hours ago, shynung said:
I'd suggest using an aeroshell designed like a wingless Space Shuttle Orbiter, with cargo doors enclosing an unpressurized cargo bay, and a heatshield on the other side. The inflatable/deflatable module is connected to a rigid pressurized module by a swinging joint - to inflate the module, the joint swings the module out of the cargo bay (still attached to the rigid module via a pressurized tunnel/walkway), then inflate after the module is clear of the cargo bay. Stowing the module would be the opposite - deflate, swing-in, the close the cargo bay doors.
Then, of course, we must compare the mass of that whole aeroshell and hinged stow assembly against the fuel that would be required for simply burning to orbital insertion. Aerocapture (using the atmosphere to insert from a hyperbolic swingby to an elliptic orbit, then circularizing once around) is a tricky thing; I have done it plenty of times in KSP but doing it IRL is rather challenging; I don't believe it has ever been done. Aerobraking to EDL, yes, but no actual aerocaptures into orbit.
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10 minutes ago, tater said:
TOTO is Temperature Oxygen Tank Outlet, apparently.
Daggone LOX tanks.
If temperature at the first-stage LOX vent was out of the expected range, does that mean more stubborn LOX/COPV issues?
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I guess it's 1.5-body.
That is, large objects like planets and moons are on rails, but everything else reacts accordingly. Doesn't account for satellite mass.
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I, for one, suspect uprating of the Merlin 1Ds in anticipation of Block 5.
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And here...we...go!
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1 hour ago, tater said:
I'd think that the engine out abort modes need to be reconsidered in a more aircraft way. Airliners have engine out capability. Spacecraft with multiple engines seems to make the most sense, and dump the free return. Use a Centaur, those things are pretty bulletproof.
Another goofy idea, and too kerbal for reality, but what the heck. If you used a LV with a good upper stage, and landing/reuse of that is a pain, why not reuse it in space.
Instead of the mass required for landing S2, you make a similar adapter that is in fact designed for docking and propellant transfer. Note that it might require EVA, that's fine. The design might have the docking/transfer stuff exit to the side, so it's not a nose to nose type docking. You collect the stages where your craft is (say stuff you are sending ahead to Mars), and the upper stages are ganged to form a transfer stage for departure. At some point after they are connected and pressure tested, you send up tankers. You now have a few Merlin-1DV engines, or Be-4U engines as your departure stage.
That's not too kerbal for reality at all. My proposed mini-ITS upper stage with two dev Raptors? Precisely the transfer vehicle I was considering to use for this. 141-tonne propellant tank, two 1100-kN engines, 130 cubic meters of payload space, and auxiliary thrusters capable of landing 40+ tonnes on Mars after a lifting-body re-entry. Perfect.
Propellant transfer port on the side or wing; docking port on the nose. Who cares if you have to switch back and forth? We have been docking spacecraft with the ISS for decades now; it requires some doing, but it is a solved problem.
All the ISRU proposals I have seen are ridiculously limited, because you have to somehow integrate a separate crew capsule. Why on Earth (or Mars, as the case may be) would you want to do that?? Make the ISRU unit self-contained and reusable, and send it up to Martian orbit to refuel your lander. Your lander needs fuel to land, after all, and it is a lot easier to do an RCS-assisted docking and fuel transfer in orbit than it is to try and do a fuel transfer via EVA.
You're going to need those high-specific-impulse, high-thrust chemical propellant engines to get off Mars, so why not use them for your transfer?
1 hour ago, tater said:There is nothing we could tell NASA they haven't thought of. Docking upper stages (say F9 US) is something that might be more of a kooky SX idea.
I'm sure NASA has thought of docking upper stages, but consideration of propellant transfer might be a little low on their priority list, and reversible propellant transfer moreso.
I haven't run all the numbers, but back-of-the-envelope estimates suggests at least ten times more TMI propellant is needed for a straight chemical Mars Orbit Rendezvous than would be required for an aerobrake-assisted Mars Orbit Rendezvous.
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33 minutes ago, radonek said:
And reliability.
And crew safety.
Crap, I totally forgot about this.
Strapping people to continuously exploding bombs and blasting them up so fast that they miss the Earth when they fall back down is, by definition, rather risky. But doing it Shuttle-style is one of the poorest ways to do it.
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7 minutes ago, tater said:
Or you bring the 2km/s worth of props.
If you have a Martian Orbit Rendezvous mission architecture (the Mars equivalent of the LOR used by Apollo) and the ability to transfer propellant on orbit, there's a neat trick you can use to beat the rocket equation. Launch your service module, your expandable hab, and your lander/crew module into LEO, fuel them all, and dock them together. Use your service module's engines to perform the TMI.
Continue along your lazy transfer to Mars, making full use of your nice roomy hab. However, immediately before reaching Mars, physically transfer all your consumables from the hab into the lander. Disconnect the lander from the hab, and use the lander to aerocapture into low Martian orbit while the service module uses the last of its fuel reserves to do an orbital injection burn, still attached to the hab.
Once both the lander and the service module are in orbit, they can rendezvous and dock again. The lander will then transfer all but a few days' worth of consumables into the hab, and transfer all but the bare minimum of its fuel into the service module's tanks.
The lander then disconnects, enters, and lands. After the mission is complete, it returns to orbit with the last of its remaining fuel. It does a rendezvous with the hab and service module. All the remaining fuel from the service module is transferred back to the lander's tanks, and then the service module is jettisoned. The lander propels itself and the hab back to Earth with the same engines it used for Mars ascent.
In this way, you get the advantage of having an expandable hab on both legs of the journey, but you don't have to carry nearly as much propellant, because the propellant used for your return trip enters Mars orbit via aerocapture, but stays in Mars orbit in the service module's tanks while the lander executes its mission. Same with consumables.
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1 hour ago, shynung said:
You can get around this by having a deflatable expandable module, and a rigid flight deck. Just before aerobraking, the crew goes to the flight deck and strap themselves, while the expandable module retracts (care must be taken to not leave free-floating items that may damage the module).
IDK if the BEAM module can be deflated and neatly folded after deployment, though. Might need some more development on that front.
The BEAM's expansion is a onetime affair, so you'd need a complete redesign. Also, getting an expandable module inside an aeroshell is a tricky affair. The expandable module will have to be docked to a pressurized module while expanded, but will have to be deflated and removed from that module in order to be stowed inside an unpressurized cargo bay, but one which can be protected during aerobraking or re-entry.
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45 minutes ago, tater said:
4.41 km/s earth departure. 1.93km/s mars insertion, 4.15km/s mars departure. 18 km/s reentry velocity.
How big does a Mars transfer vehicle need to be? BA330 size for a 1 year trip? Bigger?
Any mission that minimizes duration is going to sacrifice free return. I have no idea what NASA safety requirements are, but any of the over propulsion ideas are predicated on a non-free turn anyway (VASIMR, etc). So maybe they do a cost benefit on risk. Maybe a clustered engine system (so you can deal with engine outs by a longer burn), combined with the lower radiation exposure is worth the risk of a failure to insert at Mars. A departure failure is fatal, regardless. A failure in the middle of Mars orbital insertion is also fatal. Free return only buys you peace of mind if there is a failure after the TMI, but before you do anything else. Maybe it's mitigated by a 3X shorter trip.
Transfer vehicle size is a tricky thing. There's a minimum amount of physical activity space you're going to need to keep the crew from literally going crazy for any mission longer than a couple of weeks; the activity space is not necessarily going to go up very much based on mission duration. You're also going to need a certain amount of pressurized space to store consumables; this is going to increase significantly with mission duration.
Going expandable, like BA330, is the easiest way to get a big activity space. But you can't aerobrake an expandable module, and aerobraking is the only way you can do it without essentially doing a whole Mars Cycler.
My thought is that you build the activity space into something that can aerobrake, and use expandable modules (like BEAM) to store outgoing consumables. That way, you can doing a free-return on the outgoing leg, taking your sweet time to get to Mars, and then dump the expandable modules and aerobrake at Mars. You can then take a high-energy, low-transit-time return with as little mass as possible.
The mini-ITS concept I've been working on has a crew cabin volume of about 130 cubic meters. I was thinking they would go two at a time, each with two crew and a couple of BEAM modules docked in to store pressurized consumables, on a slow outgoing trip. Once at Mars, they'd dump the BEAMs, aerobrake, rendezvous, and transfer all but the barest fuel and consumables to the one remaining in orbit. The other vehicle would enter, land, complete the mission, and return to orbit. Both would refuel in orbit, using a previously-sent tanker or a previously-sent ISRU ship, and head home on the highest-energy transfer they could manage.
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1 hour ago, tater said:
OK, I figured out what I did. Set max duration to 2 years.
You can do a round trip Mars mission in the right years in under 400 days in 2018, 2033 with an Earth reentry speed of ~15km/s. That includes 30 days at Mars.
Most of the 2020 short duration missions all require entries back home ~19km/s, though. Short duration in 2022 all have 20km/s+ entires on return. 2031 is a good year to leave on a fast trip. Barely over a year total, and ~16km/s reentries.
How much dV do you need for the TMI, and how much dV do you need out of Martian orbit?
Trying to figure out whether it would be better to go ISRU-ahead or tanker only.
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9 hours ago, tater said:
A mission is possible in ~1.25 years (30 day stay on surface) total duration, but the Earth entry is on the order of 20km/s, with a total dv from LEO on the order of 9 km/s. More fuel decreases required supplies, but of course a higher velocity transfer kills the free returns.
Wait, how are you getting 9 km/s? I'm getting 10.2-10.6 minimum for the round-trip, assuming aerobraking direct from a minimum-dV Hohmann transfer at both ends.
If fully-refueled in LEO, my mini-ITS can deliver 69 tonnes to Mars orbit via aerocapture and 47 tonnes to the Martian surface with propulsive landing. One mission profile I like is to put fuel in Martian orbit, either by sending a tanker along or by sending an ISRU-equipped lander ahead to land on Mars, make the fuel, and return to Martian orbit. That should be able to permit speedy transfers both ways.
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22 minutes ago, magnemoe said:
Shuttle had too large cargo capacity for manned missions. I would reduce that to unpressurized cargo, optional arm and air lock. Then have an unmanned mission.
The mini ITS some presented here would be pretty much perfect. Might even do an unmanned version with an larger cargo hold for satellite launches.Why thank you, I agree that it is pretty much perfect.
I was already planning on three variants: one with a crew cabin and no unpressurized cargo bay, one unmanned with a cargo bay/fold-away fairing, and one that is just a tanker. The math works really ridiculously well.
SpoilerJust because I'm a little thrilled with the design right now, here are the payloads I've got at present:
LEO GTO ISS Falcon 9FT (RTLS) 20.6 4.0 5.5 Falcon 9FT (OCISLY) 22.4 5.0 7.2 Falcon 9FT (expended) 25.7 6.7 10.1 Falcon Heavy (recovered) 41.0 13.1 23.0 Falcon Heavy (core expended) 49.1 16.2 30.3 Falcon Heavy (expended) 61.4 23.2 41.0 "LEO" and "GTO" are the unmanned cargo variety, with full recovery for the upper stage. Conveniently, the payload penalty for upper-stage recovery is the same for LEO missions as for GTO missions, since a lifting-body re-entry bleeds off all your velocity either way. "ISS" represents the pressurized cargo capacity to the ISS orbit and inclination from a KSC launch, with the crew cabin installed and a notional dry mass of 20.5 tonnes. The tanker (not included or referenced in the table) can get to LEO on a fully-recoverable Falcon Heavy with 40 tonnes of propellant, plus its own landing reserves.
For getting BLEO, on-orbit refueling gives us some fantastic capabilities. From this thread:
QuoteNotionally, consider the following plan for a Mars Sample Return mission:
Two-tonne rover capable of acquiring samples is launched to LEO in the cargo-variant upper stage. A tanker-variant upper stage is also launched to LEO. Both are fully refueled in orbit and exit together on TMI. After the TMI burn, the mission spacecraft has 35 tonnes of propellant remaining; the tanker has 55 tonnes of propellant remaining.
Immediately after the TMI burn, the two upper stages rendezvous and the tanker transfers 53 tonnes of propellant to the mission spacecraft, then adjusts its trajectory to perform a Martian free-return. It will have enough residuals for high-energy Earth EDL after its loop around Mars. The mission spacecraft is now 62% fueled, with 88 tonnes of propellant.
The mission spacecraft performs a high-energy entry and landing on Mars, reaching the surface on its auxiliary thrusters with 69 tonnes of propellant. The rover exits and picks up a series of samples, then returns to the mission spacecraft.
The mission spacecraft lifts off on its thrusters, fires its main engines, and rockets toward the solset on a direct ascent to Earth Injection. It performs a high-energy entry and lands on Earth with 5 tonnes of propellant to spare.
Fully-reusable Mars Sample Return with no ISRU required, at the cost of only two reusable Falcon-family launches plus refueling runs.
Adapting the same mission plan as before, but for a crewed lunar mission:
Fully-fueled manned vehicle (dry mass 20.5 tonnes, payload 4 tonnes including crew) and tanker head for TLI out of LEO together as before, with the tanker transferring its propellant reserves to the manned vehicle immediately after the TLI burn and coming back on a free-return trajectory to land. Manned vehicle reaches cislunar space with 112.8 tonnes of propellant, executes orbital entry, deorbit, and landing to reach New Tranquility Base with 48.8 tonnes of propellant remaining.
After the lunar sortie (which can last quite a while, given that total delivered payload is the same as the entire gross mass of the Apollo Lunar Ascent Module), the manned vehicle lifts off on its thrusters, ignites its main engines, and heads on a direct ascent to Earth. EDL is completed with a whopping 10.2 tonnes of propellant to spare.Speaking of which, do you have a procedural parts mod, by any chance? I only have the demo, obviously without mods, so as much as I'd like to build a mockup of the mini-ITS, I cannot. I suppose I could do it in Google Sketchup, but then I couldn't do any simulated EDS goodness.
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10 hours ago, tater said:
I wonder what the maximum direct entry speed could be for an Earth reentry, anyone know?
SpaceX lists the Earth re-entry as 12.5 km/s or a bit more, but with peak acceleration at 3 gees. Mars entry is lower, at 8.5 km/s, but you end up with up to 6 gees due to the thinner atmosphere.
9 hours ago, YNM said:Too long time -> lots of consumables.
Shorter time -> more fuel.
I know this might sounds crazy, but how far can we tradeoff from each other there ? I mean, if you carry lots of fuel it can't really spoil (and faster mission benefits from less loss as well), so what do you think ? Is anyone willing to really, really run the numbers ?
The ITS presentation had a lot of these numbers provided -- delta v vs payload. So you can start there. One of the issues is mission duration.
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57 minutes ago, Yobobhi said:
But the Shuttle could carry a lot more mass to orbit than many other launchers, AND had extra capabilities. Its only handicap was cost.
And launch frequency.
And the requirement of a crew.
And availability.
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If we're limiting ourselves to Kinetic Projectile Weapons delivered via re-entry, what are the advantages and disadvantages of using elliptical vs circular orbits? If you use a significantly elliptical orbit (e.g., Molniya), you can do plane changes and adjust your re-entry trajectory for very little dV, allowing you to hit a wide variety of targets. You also can have your platform's closest approach over friendly territory. But this significantly increases your lag from strike order to impact, making its military applications more limited.
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27 minutes ago, kerbiloid said:
Or they can rename some moon to Arena and begin dropping different microbiological cultures over its surface, taking bets like "who wins?", "how long it survives until extinction?", "will Marsococci and Encelophagi marry and have kids?"
This will make the experiment self-sustainable and even profitable.
All you need is some GoPro bots with a long, long operational lifetime...
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13 minutes ago, Bill Phil said:
The largest limitation to turnaround time was actually how long it took to build the EXTs. Those are huge, and they have to rebuild them each launch. Increasing production capacity of EXTs will still leave a fairly long turnaround time. This is why we'd need a larger fleet of orbiters to get more launches per year.
If you do the same engines-on-orbiter design, but use a series of boosters that take the same fuel as your orbiter's main engines, then you can crossfeed from your boosters to your orbiter and recover the boosters by chute/flyback/hoverslam. In cases where you don't need to loft unpressurized cargo, you can drop an auxiliary tank into your payload bay and dispense with a couple of the boosters.
Tripropellant engines might be particularly useful for this.
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10 hours ago, Bill Phil said:
The trouble with the shuttle wasn't so much in design (albeit there were issues there) but in something a bit more mundane. Infrastructure. One VAB. Only a few runways long enough. Few launchpads. One facility that could build EXTs. What they needed was a whole lot more infrastructure to support high flight rates. That and a much larger fleet. They developed the shuttle too inexpensively.
Shuttle-C would've helped a lot as well.
Do you think they could have improved turnaround with a higher flight rate? Seems like a lot of the design choices ended up making refurbishment just ridiculously lengthy.
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23 minutes ago, tater said:
No kidding, this thread lost 30+ hours of posts.
I'm seeing Nibb as the author of maybe a dozen posts, including some of mine, all merged into one.
I made a thread to report the issue, and the thread disappeared, lol.
On topic, SLS delayed until at least early 2019:
Oh, I see what you mean! My replies are actually here, but merged into Nibb's post.
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IIRC there was a tongue-in-cheek explanation of this: first they give you a gentle reminder, then they give you a louder, less pleasant "buckle in or else", and then you get forcefully placed on the floor. By acceleration. But I doubt it would hurt you significantly. No worse than a fender-bender.
There's a week or two of training.
What is it with the weird staging of the ISRO GSLV?
in Science & Spaceflight
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Precisely. Keeping it there gives a central thrust column, if nothing else.