totm nov 2023 SpaceX Discussion Thread

[tater]

 

[mikegarrison]

1 hour ago, cubinator said:

The Dragon heat shield is definitely designed to fly multiple times without being replaced. It should be thick enough for a few reentries.

I thought they replace it every time.

[RCgothic]

4 hours ago, mikegarrison said:

I thought they replace it every time.

I thought I'd heard that each heat shield could withstand multiple re-entries, but I can't substantiate where I got that from now ¯\_(ツ)_/¯

[sevenperforce]

1 hour ago, RCgothic said:

I thought I'd heard that each heat shield could withstand multiple re-entries, but I can't substantiate where I got that from now ¯\_(ツ)_/¯

Probably from this article...

https://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?page=2

“In fact, says Musk, a single PICA-X heat shield could withstand hundreds of returns from low Earth orbit; it can also handle the much higher energy reentries from the moon or Mars.”

This was a long time ago and was in reference to the heat shield on Dragon 1. Probably some light exaggeration here by Musk.

Presently, crew dragon and cargo dragon heat shields are single-use, not because they could not be reused, but because saltwater incursion tends to ruin them.

[Beccab]

The Claw is on the move! QD arm is likely to be completed in a couple days

[MKI]

3 hours ago, sevenperforce said:

Presently, crew dragon and cargo dragon heat shields are single-use, not because they could not be reused, but because saltwater incursion tends to ruin them.

Dragon heat shield be like:

Re-entering Earths atmosphere multiple times easy.

Dealing with the most common surface area on Earth hard.

 

 

[wumpus]

4 hours ago, sevenperforce said:

Probably from this article...

https://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?page=2

“In fact, says Musk, a single PICA-X heat shield could withstand hundreds of returns from low Earth orbit; it can also handle the much higher energy reentries from the moon or Mars.”

This was a long time ago and was in reference to the heat shield on Dragon 1. Probably some light exaggeration here by Musk.

Presently, crew dragon and cargo dragon heat shields are single-use, not because they could not be reused, but because saltwater incursion tends to ruin them.

While that was the agreement during the first flight, NASA has relented and allows reuse.

https://spacenews.com/spacex-to-reuse-dragon-capsules-on-cargo-missions/

https://spaceflightnow.com/2020/06/23/nasa-agrees-to-fly-astronauts-on-reused-crew-dragon-spacecraft/

[no idea of the quality of the links,  but I'm pretty sure I'd heard they  were re-using them for cargo].

[magnemoe]

22 minutes ago, wumpus said:

While that was the agreement during the first flight, NASA has relented and allows reuse.

https://spacenews.com/spacex-to-reuse-dragon-capsules-on-cargo-missions/

https://spaceflightnow.com/2020/06/23/nasa-agrees-to-fly-astronauts-on-reused-crew-dragon-spacecraft/

[no idea of the quality of the links,  but I'm pretty sure I'd heard they  were re-using them for cargo].

This is reuse of capsule not heat shield. Now could the  PICA-X heat shield be used on starship if it is so good? Is it heavier or is it other issues seeing they had tile problems. 
Or would the get the same problem with starship as it will flex a to much compared to the capsules so you need tiles anyway?

[sevenperforce]

34 minutes ago, wumpus said:

While that was the agreement during the first flight, NASA has relented and allows reuse.

https://spacenews.com/spacex-to-reuse-dragon-capsules-on-cargo-missions/

https://spaceflightnow.com/2020/06/23/nasa-agrees-to-fly-astronauts-on-reused-crew-dragon-spacecraft/

[no idea of the quality of the links,  but I'm pretty sure I'd heard they  were re-using them for cargo].

NASA will now allow crew to be launched on both reused capsules and reused boosters. However, the heat shielding will be replaced between each flight, so the capsules will look brand new each time. The bottom of the capsule is not the only heat shield; the aeroshell also has ablative shielding.

9 minutes ago, magnemoe said:

This is reuse of capsule not heat shield. Now could the  PICA-X heat shield be used on starship if it is so good? Is it heavier or is it other issues seeing they had tile problems. 
Or would the get the same problem with starship as it will flex a to much compared to the capsules so you need tiles anyway?

They were originally planning on using PICA-X for Starship back when it was still going to be carbon-fiber. It would have eroded over time but slowly, at least for LEO fueling flights. Starship is much fluffier than a capsule so the load on the heat shield would have been lower.

But once they switched to stainless steel, the acceptable substructure temperature came way up, meaning that they could afford to use non-ablative silica tiles which weigh much much less. This approach is more like the “hot structure” plan for Dyna-Soar.

[tater]

The reporting has said that Isaacson paid "under $200M" for the flight, yet we also know that NASA pays more than that on a per seat basis ($53M?) per the contracted launches into the total contract amount. I suppose that since it was fixed price, that includes development though, so it's hard to sort out.

Presumably they might have used a different number in the press reports if it was far, far lower than $200M, so we'll have to assume it's maybe at least close to that?

Amazing that they might have a market to manufacture Dragons just for civilian flights.

 

[Beccab]

3 minutes ago, tater said:

The reporting has said that Isaacson paid "under $200M" for the flight, yet we also know that NASA pays more than that on a per seat basis ($53M?) per the contracted launches into the total contract amount. I suppose that since it was fixed price, that includes development though, so it's hard to sort out.

Presumably they might have used a different number in the press reports if it was far, far lower than $200M, so we'll have to assume it's maybe at least close to that?

Amazing that they might have a market to manufacture Dragons just for civilian flights.

 

Also worth noting the article says the future free flying dragon missions will be 40 millions per seat, possibly lower. On the other hand the Dragon mission Axiom 1 will cost roughly 50 millions per seat iirc, but that is including all the additional costs of dealing with NASA and ISS as well as for staying there for days

[tater]

1 minute ago, Beccab said:

Also worth noting the article says the future free flying dragon missions will be 40 millions per seat, possibly lower. On the other hand the Dragon mission Axiom 1 will cost roughly 50 millions per seat iirc, but that is including all the additional costs of dealing with NASA and ISS as well as for staying there for days

I think they also move some mass of cargo with the ISS flights, including perhaps trunk cargo? Maybe the total price goes up, and the per seat cost doesn't include the fact some payload is cargo?

[RealKerbal3x]

39 minutes ago, tater said:

I think they also move some mass of cargo with the ISS flights, including perhaps trunk cargo? Maybe the total price goes up, and the per seat cost doesn't include the fact some payload is cargo?

They might carry some cargo along with them in the capsule, but I believe they can't carry anything in the trunk on crew missions due to CoM issues in a potential launch abort.

Edited September 20, 2021 by RealKerbal3x

[Brotoro]

31 minutes ago, RealKerbal3x said:

They might carry some cargo along with them in the capsule, but I believe they can't carry anything in the trunk on crew missions due to CoM issues in a potential launch abort.

But a tiny cargo should be OK. I would think a microsat that could be released to circle around the Dragon taking pictures of the ship (and me in the observation cupola dome) would be cool.

[Codraroll]

2 hours ago, Brotoro said:

But a tiny cargo should be OK. I would think a microsat that could be released to circle around the Dragon taking pictures of the ship (and me in the observation cupola dome) would be cool.

Circling around the Dragon wouldn't be easy in practice, though. It would need a thruster (complicated), or a tether (also complicated). Technically, the mass of the capsule generates a small gravitational field, so the capsule has a small sphere of influence it would be possible to orbit within, but unfortunately that sphere of influence would be about the size of a tennis ball around the centre of mass. Any wider orbit than that would reach escape velocity. Except that this also assumes all the mass of the capsule is concentrated in one point, which I don't think is the case in reality.

[cubinator]

3 hours ago, Codraroll said:

Circling around the Dragon wouldn't be easy in practice, though. It would need a thruster (complicated)

I feel like we're at a level of technology where we could make a drone like that. In fact, they have a bunch of similar things on the ISS right now, they are functionally the same except I think they use little fans to fly around the pressurized area. If you play it right, you can get the centripetal force of going around Earth to do most of the work for you, looping around slowly. I bet it wouldn't be too hard to make a little gizmo with enough juice to not get lost doing a couple donuts around the ship. Carry a spare deorbit-stick if there's concern.

Edited September 21, 2021 by cubinator

[MKI]

If the requirements are to examine the capsule from the outside, you only really need a small camera you can detach, then have the capsule do the "maneuvering". The camera's job would just need to be able to see and possibly rotate to keep orientation. However, the "seeing" part means you might need a pretty decent camera, which costs $, and still weighs something.

If you can put a camera on a Telsa and launch it past the orbit of Mars as a demonstration, I'm sure you can do the same to get some neat shots of Dragon in orbit. But like anything weigh is still expensive, so you'd need a good reason to do it. There's already a camera in the trunk to observe stage separation, but as most streams show, it can't see anything after a few second. Getting a camera out of the trunk have it "stick around" and then have Dragon be observed later might be high risk = low reward, when the reward is a picture, and the risk is bashing into something.

[sevenperforce]

37 minutes ago, MKI said:

If the requirements are to examine the capsule from the outside, you only really need a small camera you can detach, then have the capsule do the "maneuvering". The camera's job would just need to be able to see and possibly rotate to keep orientation.

Really good point on the capsule doing the maneuvering. However, pointing is still an issue. The camera would need a reaction wheel.

I mean, I suppose they could simply toss a single starlink into the trunk and use that.

[tater]

39 minutes ago, MKI said:

Getting a camera out of the trunk have it "stick around" and then have Dragon be observed later might be high risk = low reward, when the reward is a picture, and the risk is bashing into something.

The time to do it would be after ISS, OTW home. Camera drone could have a thruster for deorbiting itself. Yeah, more mass, but save it for a mission with no cargo, it's still only a few kg (use regular off the shelf wifi, since it's not going far).

Edited September 21, 2021 by tater

[CatastrophicFailure]

53 minutes ago, MKI said:

Getting a camera out of the trunk have it "stick around" and then have Dragon be observed later might be high risk = low reward, when the reward is a picture, and the risk is bashing into something.

Bingo. 

It’s a really, really cool concept, but most things related to crewed spaceflight don’t respond well to being bumped. I think the Chinese Mars lander actually did something like this, ejecting a tiny camera bot to take pics after it was on its way, but that’s a much lower risk situation when it’s constantly getting farther away and not doing anything… complicated. 

[Beccab]

Didn't they have a free flyer like that in a couple of the later Shuttle missions? I'm not even sure if it had a camera though

[JoeSchmuckatelli]

First time SX has to deal with a billionaire who feels she's too 'special' to put herself through the stuff these tourists did (making it more mission-like than vacation-like) --- that will be the end of their tourism business.  "Fly me up there so I can say I did it" crowd will be just like the people who endanger themselves and others every year on Everest. 

 

 

Except that people survive Everest.

[mikegarrison]

31 minutes ago, JoeSchmuckatelli said:

First time SX has to deal with a billionaire who feels she's too 'special' to put herself through the stuff these tourists did (making it more mission-like than vacation-like) --- that will be the end of their tourism business.

Not for enough money. It's the golden rule. I'm sure that for enough money you could hire SpaceX to not only launch you up there but to send up a waiter who fed you grapes whenever you felt like it.

Mainly what SpaceX did with this mission was defuse (a little bit) the "billionaires in space" pushback, by sending up a crew of people who mostly didn't actually pay to go (and also had sick kids cheering for them).

[tater]

 

Yet more reason for some sort of orbital module. Put a cupola, and a toilet on that, dock Dragon to it.

If leaving a crew SS test article in LEO seems like a bad idea (and I can see a few reasons it would be), they could launch a smaller test module. Maybe use the same mold line as the fairing, only it's a hab to test new life support tech, toilets, etc.

Edited September 21, 2021 by tater

[mikegarrison]

Space toilets have long been one of the really difficult parts of human life support to get working well. The new ISS toilet sent up last year supposedly cost $23M to develop and build.

Side note: I worked with a guy who was part of the development process for a new toilet in airplanes. If you are old enough you probably remember airplane toilets that were basically big buckets full of human waste and that blue chemical, and if they got full then they got full. (It was not widely advertised, but that blue chemical was actually recirculated. So when you flushed with it by the end of the flight, it was not *just* blue chemical....)

Well, when we switched to vacuum lavs, that went away. Our toilets now all connect to a central tank, which is kept at a pressure lower than the cabin pressure. So a person uses the toilet and presses the lever. A valve opens up and the pressure differential sucks the material away to the tank. You never get individual toilets that fill up (although you could get the entire system to fill up).

Anyway, I worked in the noise group, and the guy I worked with was trying to measure the noise the toilet would make when it flushed. We wanted enough suction to suck things, but not so much it was scary to the user.

To test these in the lab, they apparently used a mixture of liquid (just water, I think) and fake turds. They were made of something like peanut butter and dried dog food and some other ingredients that when mixed together and shaped into logs had the expected consistency, stickiness, and other mechanical properties.

Edited September 21, 2021 by mikegarrison