Is it possible to do a direct accent mission to the moon?

[tater]

1 minute ago, DerekL1963 said:

If it stops in orbit, it's not Direct Ascent... 

As I said, yes and no. As I understand it, back in the day refilling props wasn't even on the table, they were talking about assembling spacecraft in Earth orbit with separate launches vs having a separate lander (LoR), and CM as lander (Direct Ascent). That said, at the time the concern was about rendezvous in general, not just assembly, so rendezvous for filling would have applied then I guess (as a problem), but it was a problem that turned out to be baseless (rendezvous happens with literally every human spaceflight for decades now).

So in the context of the time period, you are certainly correct, but Starship is kind of a new paradigm. I guess strictly speaking I don't see it as EoR in the way that was used in the Apollo era (assembling separate spacecraft components in LEO), but it's not Direct Ascent in the Apollo-era sense, either, clearly. It's is Direct Ascent to the extent that the whole craft lands on the lunar surface, and a component of that craft then returns to Earth (in this case that component is the entire craft, not just a stage). I have to admit I personally think of "Direct Ascent" as describing the lunar phase of the mission---not lunar orbit rendezvous, you ascend from the moon, and proceed directly back to Earth.

It needs a new phrase, I guess, since the stack as launched goes to the Moon, but a different stack transfers propellant.

 

[DDE]

15 minutes ago, Bill Phil said:

Yeah, but imagine the damage if the thing exploded? That stuff is toxic... thousands of tonnes of it probably isn't a recipe for success - let alone flying people on it.

Sounds like a job for Program 7 to thermally decontaminate!

[kerbiloid]

From wiki _{(sorry if this violates somebody's moral principles, lol)}.

LC50 * t, ppm * hr:
NTO: 57.5 * 4 = 230 (rat)
UDMH: 252 * 4 = 1000 (rat), 172 * 4 = 700 (mouse)
Hydrazine: 260 * 4 = 1000 (rat), 252 * 4 = 1000 (mouse)
Phosgene: 340 * 0.5 = 170 (rat), 438 * 0.5 = 220 (mouse)
Hydrogen Cyanide: 500 * 5/60 = 40 (rat), 323 * 5/60 = 30 (mouse)

So,  LC50 of NTO : UDMH : Hydrazine : Phosgene : Hydrogen Cyanide ~= 6 : 25 : 25 : 6 : 1

Launch mass:
UR-700: = 5 000 t
"UR-700M": 16 000 t.
Propellant ~ 93%
Oxidizer:Fuel ratio ~= 2.7.

So:
UR-700:
UDMH = 5000 * 0.93 / 3.7 ~= 1300 t;
NTO = 5000 * 0.93 / 3.7 * 2.7 ~= 3400 t;

UR-700M:
UDMH = 16000 * 0.93 / 3.7  ~= 4000 t;
NTO = 16000 * 0.93 / 3.7 * 2.7 ~= 11000 t;

Global production of hydrazine hydrate: ~200 000 t/y. So, ~100 000 t of hydrazine.
Transportation - in 40..60 t cysterns.
UDMH of UR-700 ~1% of global hydrazine production, ~30 cysterns = 1 train.
UDMH of UR-700M ~2.5% of global hydrazine production, ~80 cysterns = 2 trains.

So, UR-700(M) are just one of tens-to-hundred trains transporting it across the world.

Total toxicity, scaled to Phosgene and H.Cyanide.

Phosgene:
UR-700 = 1300 * 6 / 25 + 3400 * 6/6 = 3 700 t
UR-700M = 4000 * 6 / 25 + 11000 * 6/6 = 12 000 t
Global production of phosgene: 8.5 mln t/y

H.Cyan.:
UR-700 = 1300 * 1 / 25 + 3400 * 1/6 = 620 t
UR-700M = 4000 * 1 / 25 + 11000 * 1/6 = 2 000 t
Global production of h.cyanide: ~500 000 t/y (USA only).

So, the UR-700 and even -700M toxicity is negligible compared to any chemical plant which are placed right next to big cities.

And unlike the Phosgene and Hydrogen Cyanide, these UDMH and NTO would mostly burn right in the RUD event, so the unreacted remains would unlikely exceed several cysterns.

So, no need in nukes (though I like the idea).

UR-700 was the thing.

[DDE]

4 hours ago, kerbiloid said:

So, the UR-700 and even -700M toxicity is negligible compared to any chemical plant which are placed right next to big cities.

And fluorine is even less nasty, as Glushko argued when discussing the roll-out of RD-301.

[DerekL1963]

8 hours ago, tater said:

they were talking about assembling spacecraft in Earth orbit with separate launches vs having a separate lander (LoR), and CM as lander (Direct Ascent).

Direct Ascent means going directly from one body to another without an interim stop in parking orbit.  Nothing more, nothing less.

[tater]

Then no direct ascent was ever even on the table. Any Apollo mission would have established orbit to make sure everything was fine before TLI.

Edited May 31, 2019 by tater

[tater]

Here is an analysis of the 2 Direct Ascent modes NASA considered:

Quote

The two Direct Flight Options, Fig. 3, Nova DF and C-5 DF, entail the same maneuvers with different size and capability launch vehicles. The Saturn C-5 launcher had a significantly smaller payload capability than the Liquid Nova launcher; this requires that the CSM be scaled down from a 154 in diameter to 138 in. The direct flight modes require one launch on the Liquid Nova launch vehicle or Saturn C-5 launch vehicle, respectively. After launch, the two modes are very similar to each other and to the EOR mode; the only difference is the mass and size of the hardware and there is no need for propellant transfer. After insertion into LEO, the TLIS performs the TLI maneuver, pushing the CM, SM, LTDM, and LBM towards the moon. The remainder of the mission follows the EOR mission directly.

NASA images of the era show Direct Ascent with a line going from liftoff, straight to the Moon, making it look like no LEO is first established, the EoR of course shows an orbit. The LoR, OTOH, also shows no LEO insertion before TLI (diagram identical to Direct until it gets to the Moon), which is not what was in fact done. Direct Ascent had nothing to do with the orbital parameters, it was about not having to do any rendezvous maneuvers at all to accomplish the mission (which in the Starship case makes it definitely not Direct).

I was completely wrong about EoR, however. They in fact considered refueling even back then, not just assembly. That makes Starship simply EoR as the terms were first established (though the CCCP was doing EoR via assembly).

 

 

Edited May 31, 2019 by tater

[Guest]

On 5/29/2019 at 9:16 AM, DDE said:

Max Faget

[DerekL1963]

3 hours ago, tater said:

Then no direct ascent was ever even on the table. Any Apollo mission would have established orbit to make sure everything was fine before TLI.

Well, no.  In the beginning, it was the same trajectory that Ranger and Surveyor (and many non-lunar missions used) used - right from the pad to the moon.  The name (which comes from orbital mechanics) persisted even as technology/capabilities increased to the point where a parking orbit was feasible to plan for.  (You need restartable engines, more battery capacity, ullage engines and attitude control, a guidance system that will be stable enough long enough, etc... etc..)

[kerbiloid]

Wasn't the Apollo engine overpowered exactly because originally it was purposed for direct ascent?

[DDE]

6 hours ago, tater said:

Liquid Nova

I’d love to see a solid Nova.

3 hours ago, Aperture Science said:

Oh, funny you’d mention the Heavy.

I’m raising you a pile of expended Fagots.

Edited May 31, 2019 by DDE
Link to r/SyrianCirclejerkWar is a violation of Rule 2

[kerbiloid]

A solid-fuel OTRAG made of a bunch of the spent Fagots refueled with powder?

[tater]

8 hours ago, DerekL1963 said:

Well, no.  In the beginning, it was the same trajectory that Ranger and Surveyor (and many non-lunar missions used) used - right from the pad to the moon.  The name (which comes from orbital mechanics) persisted even as technology/capabilities increased to the point where a parking orbit was feasible to plan for.  (You need restartable engines, more battery capacity, ullage engines and attitude control, a guidance system that will be stable enough long enough, etc... etc..)

Yeah, but they would have established orbit, anyway, with crew aboard. So they it seems like they never seriously considered human direct ascent trajectories (in the strict sense) if even Nova was supposed to check out in orbit before TLI. It's not like it even requires a restart. You can do one stage 2 burn and still establish Earth orbit. The only concern is then starting the TLI burn, which has to be done anyway. The coast phase in orbit can be arbitrarily short (it's entirely determined by the Earth-Moon geometry). Battery life (stage 3) then is largely as a plan B in case they have an issue that they can work over X orbits, else scrub TLI and head home. Clearly this is where they went with Apollo LoR (which nominally had a mission profile identical to Nova until TLI).

Ranger 7-9 used launch, coast, burn (parking orbit).

As did most of the Surveyors:

Quote

An early NASA technical report entitled “Surveyor Project Final Report4” states: Surveyors I, II, and IV were injected into translunar trajectories via the direct-ascent mode; Surveyors III, V, VI, and VII used the parking-orbit ascent mode. The parking-orbit ascent mode was clearly superior from a mission design standpoint, since, using a parking-orbit ascent, it was geometrically possible to launch on any day of the month.

Surveyor did direct lunar descent, though.

Looks like the Nova mission profile was planned to do a LOI burn, too. Easier to establish landing site (vs a straight retro burn landing where they would be aimed for lunar impact). I've always personally read "direct ascent" as referring to the rocket architecture more than orbital mechanics. Seems like this is wrong in the specifics, but not really wrong in terms of actual human mission architectures (that or Apollo direct ascent was never technically direct ascent, but something closely related). Maybe if I ever get to own Krafft Ehricke's Space Flight Vol. 2: Dynamics (it's godawful expensive, I only have Vol 1) I can check and see what the contemporary usage was technically. I have the feeling the usage actually became much more fuzzy, since they would call mission profile "direct ascent" even if the initial perigee was such that the spacecraft was in orbit from the start (need not be circular to still be a parking orbit, though they chose circular to simplify their orbital mechanics, because they could move a burn a little after X orbits (phasing), and still fly a similar profile). I have a feeling that any human mission would have started with a parking orbit once they started planning it in earnest, simply because it gives more abort options.

(should I buy Volume 2 for $165? Ugh.)

Edited May 31, 2019 by tater