totm nov 2023 SpaceX Discussion Thread

[tater]

 

[Beccab]

Looks like this wasn't posted here yet

[tater]

That was NOT the link I posted, lol. I posted the launch hazard areas for the Starlink launch in 5 days, lol. Odd.

[tater]

 

[sevenperforce]

13 hours ago, CatastrophicFailure said:

@sevenperforce ok Mr. Numbers Man, now I’m curious… as far as we know, could Atlas/Vulcan get similar lob altitudes with Starliner?

whether Starliner would actually survive the trip is NOT the topic for discussion… 

An Atlas V 401 can only put around 9.8 tonnes in LEO, but you can add up to five solid boosters. It takes two solid boosters to push the 13-tonne Starliner to an ISS orbit, but that's the limit. More boosters mean a higher staging velocity, though. The Atlas V 531 can put 15.6 tonnes into LEO just like we saw with the max-capacity Starlink launches, so the Atlas V 531 is probably comparable to Falcon 9 Block 5 at max reusable capability.

Supposedly, the Atlas V 552 (a possible configuration, though not one that has ever flown) can put 20.5 tonnes into LEO, which is close to the capability of an expendable Falcon 9 Block 5. However, that's to a different reference orbit than the others provided by ULA. The math here is actually easier than the math for Falcon 9 since the masses and propellant loads of the single-engine and dual-engine Centaur (SEC and DEC) are well-described. Moreover, ULA helpfully specifies its reference orbits.

The Atlas V 521 can send 12,510 kg to the ISS, while the Atlas N22 sends the 13-tonne Starliner to the ISS. The only difference between the two (treating drag considerations as de minimis) is the engine count, which helps with gravity drag losses. Centaur carries 20.83 tonnes of propellant and has a dry mass of 2.25 tonnes (SEC) or 2.46 tonnes (DEC). The RL10C-1 has 449.7 seconds of specific impulse, so the SEC with a 12.5-tonne payload develops 3,883 m/s of dV, while the DEC with a 13-tonne payload develops 3,763 m/s of dV. Since they are going to the same orbit, this helpfully tells us that the gravity drag savings for a payload of this mass are approximately 120 m/s by doubling the thrust (actually a little more because the staging velocity is a little lower with the DEC+Starliner, but again, de minimis).

ULA says that the Atlas V 551 can put 18,850 kg into a 200x200 km circular orbit; the 521 configuration only puts 13.5 tonnes into the same orbit. I'll treat the 200 km orbit as the minimum because even in a DEC configuration, the T/W ratio of Centaur is poor compared to F9US. Headed to this orbit, the SEC develops 3,029 m/s of dV while pushing 18.85 tonnes and 3,716 m/s of dV while pushing 13.5 tonnes. Since everything else is equal, we know that adding those three extra solid boosters results in a staging velocity that is 687 m/s higher.

This gives us what we need to evaluate the performance of a hypothetical Atlas V N52 (Starliner on top, 5 boosters, 2 RL10s) to that minimal 200x200 km staging orbit. On N22, a 13-tonne payload gets 3,763 m/s of dV, so it would reach a 200x200 km orbit with 47 m/s to spare (3,763 - 3,716) plus the extra 120 m/s it gets from lower gravity drag. Adding three solids would add another 687 m/s, so Atlas V N52 + Starliner reaches a 200x200 km parking orbit with 854 m/s left in the tank. The vis-a-vis equation tells us that adding 854 m/s of velocity onto a 6,583x6,583 km circular orbit raises the apogee to 10,548 km, or an altitude of over 4,000 km. That's not nearly as high as an expendable Falcon 9 could send Crew Dragon, but it is much higher than a reusable Falcon 9 can do and it is deep into the inner Van Allen belt.

One reason to choose a polar orbit for high-altitude Crew Dragon launches is that the apogee can always be at a very high latitude, ensuring that there is no passage through the Van Allen belts.

On a related note, I was curious to know what kind of on-orbit dV Starliner has. According to this page, Starliner's abort motors burn 700 pounds of propellant per second, and the Nov 2019 pad abort test showed a six second burn, so I will assume 4,200 pounds or 1,906 kg of useable propellant. Boeing says that the main OMS engines come from Aerojet Rocketdyne and produce 1,500 pounds of thrust each, so they are probably a larger variant of the 900 lbf R-40B bipropellant OMS engine, which has a vacuum specific impulse of 293 seconds with hypergolics. So I estimate that Starliner has about 457 m/s of dV on orbit. That's a bit more than Crew Dragon's 346 m/s (its Draco thrusters give it 300 seconds of vacuum specific impulse but it only carries 1,388 kg of propellant). I may be overestimating Starliner's onboard propellant, though; the abort engines may not fire at full thrust through the entire abort.

Edited February 15, 2022 by sevenperforce

[JoeSchmuckatelli]

12 hours ago, JoeSchmuckatelli said:

Any further info on this?

This is all I can find:

Quote

When asked about the progress toward the spacewalk suit, the crew did not say exactly how far along the design is. “There’s a fantastic team of brilliant engineers working on a spacesuit, and it’ll be really exciting to work together as their design unfolds,” Menon said. “And we’ll be certain to share more details with you as we get to that point.”

Billionaire who flew to orbit with SpaceX buys three new missions to space - The Verge

Other than that (or similar) I just find references to the bespoke suits we've seen for emergencies during pressurized flight.

[tater]

 

Given that this flight is later this year—they must have some idea bout the suits. The IVA suits are designed for a cabin pressure loss, so in terms of keeping them alive, it's gotta already be there. For EVAs of short duration I'm not sure what else they need... a sun visor, and possibly the suits slightly larger, and with an active undergarment for thermal control?

[Beccab]

 

[sevenperforce]

1 hour ago, tater said:

 

See, I just don't know how they can possibly expect to catch Starship. The booster is straightforward enough, but the ship?? There's just no way the ship can hover motionless to the point that this kind of precision is actually realizable.

Future Starships could have fold-out catch arms in that position, I suppose, but the forces would be tremendous.

1 hour ago, tater said:

Given that this flight is later this year—they must have some idea bout the suits. The IVA suits are designed for a cabin pressure loss, so in terms of keeping them alive, it's gotta already be there. For EVAs of short duration I'm not sure what else they need... a sun visor, and possibly the suits slightly larger, and with an active undergarment for thermal control?

The crew won't need to be doing a lot of the exertion and fine detail work that usually goes into ISS EVAs, so they don't need that much mobility.

The big challenge of wearing an unmodified IVA suit is not the life support -- their umbilicals can take care of that -- it's the "spread eagle" problem. With high pressure inside and no pressure outside, the fabric expands and balloons outward, forcing all the joints to open up and occupy the maximum amount of space. This forces you into a spread eagle/snow angel position; if you want to bend your joints, you have to force the air in the suit into a smaller space, which means almost every movement is like compressing a bike pump.

The atmosphere in Crew Dragon is ordinary sea level air, not pure oxygen, and I don't believe it was designed with the capability to switch it out and do a prebreathing sequence to use low-pressure oxygen. Although I suppose it's a fairly simple fix. Everything in there should be pure-oxygen-fireproof anyway.

I wonder if it would be possible to equip the IVA suits with some sort of an active-venting smart valve, so that if you attempted to compress a joint, it would automatically relieve the pressure into a reservoir, and then fill it back up once you expanded that joint back out.

Another option: not all movements cause compression. Joint rotation, for example, does not. The main movements which cause compression are adduction and flexion, with abduction and extension doing the opposite.  The ISS EVA suits use carefully-designed constant-volume fabric joints to allow abduction and extension without a change in the volume:

The trouble is that unless you have the very low pressure pure-oxygen mix that the ISS EVA suits use, the high internal pressure is going to cause those outside gores to "pop" out even during extension, which doesn't get you anywhere.

My favorite solution would be to enclose any adduction/flexion joints in an external hard shell which prevents the excess fabric from ballooning outward unless the joint is closed. Basically you would take the existing IVA suit and add what look like elbow pads, knee pads, etc. which use a combination of compression and a hard external shell to constrain the movement of the joint to a constant-volume approximation.

[Beccab]

 

With ULA out, I'd say it's pretty likely it's going to be another FH with either all boosters reusable or core one expended. Is there even another option for this? I was thinking Ariane 5 maybe, but I think all the launches are already sold and if Vulcan can't win Ariane 6 surely can't either

 

Edited February 15, 2022 by Beccab

[tater]

58 minutes ago, sevenperforce said:

See, I just don't know how they can possibly expect to catch Starship. The booster is straightforward enough, but the ship?? There's just no way the ship can hover motionless to the point that this kind of precision is actually realizable.

Future Starships could have fold-out catch arms in that position, I suppose, but the forces would be tremendous.

Yeah, I really don't grok their concept of operations for such a catch.

[sevenperforce]

27 minutes ago, Beccab said:

 

With ULA out, I'd say it's pretty likely it's going to be another FH with either all boosters reusable or core one expended. Is there even another option for this? I was thinking Ariane 5 maybe, but I think all the launches are already sold and if Vulcan can't win Ariane 6 surely can't either

 

It's not as heavy as JWST. What kind of a launch does it need? Just an escape orbit (C3=0)? 

[Beccab]

2 minutes ago, sevenperforce said:

It's not as heavy as JWST. What kind of a launch does it need? Just an escape orbit (C3=0)? 

Yeah, looks like it needs basically the same trajectory as the JWST but for 2/3 of the payload weight

 

 

Edited February 15, 2022 by Beccab

[RCgothic]

1 hour ago, sevenperforce said:

It's not as heavy as JWST. What kind of a launch does it need? Just an escape orbit (C3=0)? 

I reckon it's because Atlas isn't available and Vulcan isn't accredited.

[sevenperforce]

1 hour ago, RCgothic said:

2 hours ago, sevenperforce said:

It's not as heavy as JWST. What kind of a launch does it need? Just an escape orbit (C3=0)? 

I reckon it's because Atlas isn't available and Vulcan isn't accredited.

Well, Vulcan isn't available either, because it doesn't have any engines yet.

  

I don't know the maximum capabilities of Ariane 5, but it has sent up to 11.2 tonnes to GTO and up to 20.3 tonnes to LEO at an ISS orbit. That's 3.5 tonnes more than what an Atlas V 551 can send to the ISS and 2.2 tonnes more than what an Atlas V 551 can send to GTO.

According to NASA, the JWST required an effective apogee of approximately 1.06e6 km, which (according to the vis-a-vis equation) requires a perigee velocity of 10,970 m/s. Whether you're starting at 167 or 200 km, it doesn't make much of a difference; you need about 3.19 km/s leftover in LEO. 

The Roman Space Telescope's launch mass is 4.17 tonnes. For reference, the SEC and F9US have the following dV at full prop load with a 4.17-tonne payload:

• SEC: 6,377 m/s
• F9US: 8,972 m/s

A typical 27-degree GTO is about 2.27 km/s out of LEO, 920 m/s shy of what JWST or Roman needs. An Atlas V 421 can send 6,890 kg to GTO; in that configuration, it stages with 5.24 km/s, of which 2.97 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.41 km/s, more than enough to get Roman where it needs to go. ^{(And yes, I did the math for the Atlas V 411; it's not enough.)}

With three-core recovery, Falcon Heavy can send up to 8 metric tonnes to GTO. In that configuration, it stages with 7.89 km/s, of which 5.62 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.35 km/s, which is not quite as much as the Atlas V 421 but still enough to send Roman packing to its destination.

Or it could fly on a single-stick expendable Falcon 9 Block 5 with ease. Flying expendable, Falcon 9 beats three-core-recovery Falcon Heavy for payload to GTO.

4 minutes ago, sevenperforce said:

A typical 27-degree GTO is about 2.27 km/s out of LEO, 920 m/s shy of what JWST or Roman needs. An Atlas V 421 can send 6,890 kg to GTO; in that configuration, it stages with 5.24 km/s, of which 2.97 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.41 km/s, more than enough to get Roman where it needs to go. ^{(And yes, I did the math for the Atlas V 411; it's not enough.)}

With three-core recovery, Falcon Heavy can send up to 8 metric tonnes to GTO. In that configuration, it stages with 7.89 km/s, of which 5.62 km/s is used to reach LEO and the remainder is the 2.27 km/s used to reach GTO. With 4,170 kg on board, the remainder is 3.35 km/s, which is not quite as much as the Atlas V 421 but still enough to send Roman packing to its destination.

Note that this illustrates some of the distinctions between high-energy and low-energy orbits. For LEO (e.g., the ISS), a reusable Falcon 9 easily outperforms the Atlas V 421. But for high-energy orbits it's not even slightly competitive.

[tater]

 

[Beccab]

 

Everyday astronaut has interviewed Isaacman about the Polaris missions. The interview is pretty good, a couple key points from this are:

- The first mission is going to have a maximum ap between 810 and 930 miles, attempting to beat Gemini XI

- EVA will be at a lower altitude (310 km) for increased safety

- Polaris 3 will have people on board of Starship from launch to landing

- The main objective of Polaris 2 is to reduce risks in 3. Maybe launch in Dragon, dock to Starship and return to Dragon? If we're to take Apollo 9 as a comparison, they may also undock and do some free flight before redocking and returning

 

Edited February 16, 2022 by Beccab

[Beccab]

Forgot to post this - great view of the destacking the other day

 

[zolotiyeruki]

8 hours ago, Beccab said:

- EVA will be at a lower altitude (310 km) for increased safety

Can someone explain to me why EVA is safer at a lower altitude?  I mean, you're still inside the Van Allen belts, and if something goes wrong, you're in the same trouble at 310km as you are at 850 miles.

[kerbiloid]

The radiation belts begin  from 600..1000 km altitude.

Edited February 16, 2022 by kerbiloid

[JoeSchmuckatelli]

1 hour ago, zolotiyeruki said:

Can someone explain to me why EVA is safer at a lower altitude?  I mean, you're still inside the Van Allen belts, and if something goes wrong, you're in the same trouble at 310km as you are at 850 miles.

I thought the same thing.

Maybe its not 'safer' but actually 'cheaper' for SX to send up another ship if something goes wrong. 

(In the past this was rarely an option, but with SX's cadence, they might be able to have a 'standby' / rescue craft available)  Pure guess.

[Beccab]

54 minutes ago, zolotiyeruki said:

Can someone explain to me why EVA is safer at a lower altitude?  I mean, you're still inside the Van Allen belts, and if something goes wrong, you're in the same trouble at 310km as you are at 850 miles.

In a normal flight profile, you lower your altitude before starting the deorbit burn - iirc, the Cargo Dragons (used to? Been a while since I stopped following CRS stuff) do this when departing from the ISS. If something went wrong on an EVA while on that highly eccentric orbit you'd have to first lower your apogee quite a bit and only then do a deorbit burn not to stress the heat shield too much. By doing this EVA at that altitude instead you can directly deorbit if something happens that requires a return asap as long as there's someone ready to recover you near the splashdown zone

[insert_name]

1 hour ago, zolotiyeruki said:

Can someone explain to me why EVA is safer at a lower altitude?  I mean, you're still inside the Van Allen belts, and if something goes wrong, you're in the same trouble at 310km as you are at 850 miles.

In the interview I posted, they say that it increases the opportunities for deorbiting quickly

[JoeSchmuckatelli]

33 minutes ago, insert_name said:

In the interview I posted, they say that it increases the opportunities for deorbiting quickly

Isn't it easier to lower periapsis at apoapsis?

[NFUN]

Just now, JoeSchmuckatelli said:

Isn't it easier to lower periapsis at apoapsis?

In terms of delta-v, but that's not what you're worried about if there's an emergency. If you're burning at apoapsis it's more difficult to control where you land because you have a smaller burn window (as opposed to effectively the entire orbit) unless you want to waste the delta-v in normalizing anyway, and it takes much longer to coast to a higher apo or down, and the re-entry is sharper and more dangerous with a more elliptical orbit