SpaceX Dragon 2 Updates and Discussion - Thread 3

[meberbs]

SpaceX, NASA and Boeing have a common problem: Making sure their parachutes work

Rachael Joy  Florida Today
Published 6:00 AM EST Dec 16, 2019

Next year when SpaceX’s Dragon capsule is hurtling toward the Pacific Ocean at 540 miles per hour on its return from the International Space Station, the technology ensuring the astronauts inside land safely is a component it seems we’d have mastered by now: the parachute.

https://eu.floridatoday.com/story/tech/science/space/2019/12/16/nasa-spacex-and-boeing-struggle-overcome-parachute-issues/4177914002/

I don’t remember this quote from Elon, included in the article:

“Parachutes, they look easy but they are definitely not easy,” Elon Musk said in October at a press conference at SpaceX, “We’ve had so many engineers quit over the parachutes.”

Maybe those engineers were excited about Dragon being a propulsive landing spacecraft that many on this site gushed over and swore by...

The quote is simply wrong. FutureSpaceTourist was correct in not remembering that quote. Musk did not say that they had engineers quit over it. He said the Apollo program had engineers quit over parachutes. Actual quote is below (As best as I can transcribe, I may have misheard a word or 2, but nothing that should change the meaning, reporter must have significantly misheard).

For those that know the history of the Apollo program, it was actually one of the toughest things on the Apollo program were the parachutes. It was actually one of the toughest morale problems, because so many engineers quit over the ?different? parachutes. It was funny to read that and then have the same experience basically. I mean I don't think we had, you know, many people quit over it, but it is, it is to say like, a pretty arduous engineering job to get the parachutes right.

You can find this about 14 minutes into the video.

[Johnnyhinbos]

When it was determined that NASA wasn't going to go for propulsive landings, what was the reasoning behind SpaceX opting for water landings instead of on land?

I have a few of my own potential answers, but was hoping others could weigh in.

- "Water landings is how SpaceX has done cargo landings, so why change now". Therefore it's a fairly well understood method, even if far from ideal.

- "To land on land, non-propulsively, would require a major change to the architecture". Not fully convinced of this however - because wouldn't it be possible for the superdracos to do a micro firing to provide the landing cushioning? Hans has confirmed that propellant is brought back regardless (though see point below).

- "In the event of an abort, a water landing is highly likely, so might as well do water landings across the board". Not sure this logic holds either - as in, the same could be said for Starliner, yet Boeing nominally does land landings. One consideration is that in an abort that also ends in a land landing, is there prop margin available for the micro firing of the superdracos.

What's missing? I would think, if there's not a relatively huge amount of development to implement it, that land landings is a much more effectual way to go when the intention is to ultimately reuse the D2.

[whitelancer64]

When it was determined that NASA wasn't going to go for propulsive landings, what was the reasoning behind SpaceX opting for water landings instead of on land?

I have a few of my own potential answers, but was hoping others could weigh in.

- "Water landings is how SpaceX has done cargo landings, so why change now". Therefore it's a fairly well understood method, even if far from ideal.

- "To land on land, non-propulsively, would require a major change to the architecture". Not fully convinced of this however - because wouldn't it be possible for the superdracos to do a micro firing to provide the landing cushioning? Hans has confirmed that propellant is brought back regardless (though see point below).

- "In the event of an abort, a water landing is highly likely, so might as well do water landings across the board". Not sure this logic holds either - as in, the same could be said for Starliner, yet Boeing nominally does land landings. One consideration is that in an abort that also ends in a land landing, is there prop margin available for the micro firing of the superdracos.

What's missing? I would think, if there's not a relatively huge amount of development to implement it, that land landings is a much more effectual way to go when the intention is to ultimately reuse the D2.

I feel like the SuperDracos would be way overpowered even for a "microburst" to cushion the shock of landing. Normal Draco thrusters might be able to handle something like that. However, that aside...

As with fully propulsive landing, the problem is how to certify it for safety. It would mean a bunch of drop tests, parachute deployments, and practice landings, which SpaceX didn't want to do at that time (not knowing that there'd be a whole 'nother can of worms with the parachutes in the future).

Also firing the thrusters to soften the landing means you've got combustion residuals and unburnt fuel / oxidizer on the ground right by the crew and recovery personnel. That's a hazard nobody wants to deal with. This was one of the issues with fully propulsive landing as well.

Additionally, SpaceX deleted the landing legs after propulsive landing was cancelled, so there's no way to keep the capsule upright (not that that stops the Soyuz).

Firing the thrusters to soften the landing for a splashdown might be something thing they could do, but the water also absorbs the energy of landing, so I presume it's not worth doing.

May be worth considering that Boeing went with a fairly complex airbag system rather than to fire their thrusters to cushion the landing, presumably due to similar considerations.

[clongton]

When it was determined that NASA wasn't going to go for propulsive landings, what was the reasoning behind SpaceX opting for water landings instead of on land?

I have a few of my own potential answers, but was hoping others could weigh in.

1. "Water landings is how SpaceX has done cargo landings, so why change now". Therefore it's a fairly well understood method, even if far from ideal.

2. "To land on land, non-propulsively, would require a major change to the architecture". Not fully convinced of this however - because wouldn't it be possible for the superdracos to do a micro firing to provide the landing cushioning? Hans has confirmed that propellant is brought back regardless (though see point below).

3. "In the event of an abort, a water landing is highly likely, so might as well do water landings across the board". Not sure this logic holds either - as in, the same could be said for Starliner, yet Boeing nominally does land landings. One consideration is that in an abort that also ends in a land landing, is there prop margin available for the micro firing of the superdracos.

What's missing? I would think, if there's not a relatively huge amount of development to implement it, that land landings is a much more effectual way to go when the intention is to ultimately reuse the D2.

I relabeled them 1,2,3 for ease of reference.
1 & 2 are not the reason.
3 IS the reason, but the statement that Boeing opted for land landing for caparison is misleading.
Both SpaceX and Boeing opted for land landing. NASA did not nix land landing. It nixed propulsive landing, so the Boeing comparison is apples to oranges.
Water landing was already the secondary option so SpaceX simply made it the primary in order to meet the contract operational date requirements.

[Comga]

I feel like the SuperDracos would be way overpowered even for a "microburst" to cushion the shock of landing. Normal Draco thrusters might be able to handle something like that. However, that aside... 

Given how short some of the MVac burns are to circularize orbits, this seems a surmountable problem.
 

As with fully propulsive landing, the problem is how to certify it for safety.
It would mean a bunch of drop tests, parachute deployments, and practice landings, which SpaceX didn't want to do at that time (not knowing that there'd be a whole 'nother can of worms with the parachutes in the future).

That is the stated reason, opening themselves up to a certification process whose scope had yet to be determined.
And yes, even certifying the parachutes, which was supposedly known technology, was a "can of worms".

Also firing the thrusters to soften the landing means you've got combustion residuals and unburnt fuel / oxidizer on the ground right by the crew and recovery personnel. That's a hazard nobody wants to deal with. This was one of the issues with fully propulsive landing as well.

Possibly, but that could be handled, especially if you can drive up with lots of mitigation including hose-downs
(snip)

May be worth considering that Boeing went with a fairly complex airbag system rather than to fire their thrusters to cushion the landing, presumably due to similar considerations.

After reentry, Boeing's Starliner has no thrusters pointed down. Those were on the service module, which is ditched before atmospheric interface.

But I had another question:
Would the above arguments still hold if propulsive landing was augmented by the drogue chutes?
That is, shed much of the vertical velocity with small chutes, break from a modest rate of descent with a pair, or two pairs of Super Dracos, instead of all eight, leaving pairs for backup.

[woods170]

When it was determined that NASA wasn't going to go for propulsive landings, what was the reasoning behind SpaceX opting for water landings instead of on land?

I have a few of my own potential answers, but was hoping others could weigh in.

1. "Water landings is how SpaceX has done cargo landings, so why change now". Therefore it's a fairly well understood method, even if far from ideal.

2. "To land on land, non-propulsively, would require a major change to the architecture". Not fully convinced of this however - because wouldn't it be possible for the superdracos to do a micro firing to provide the landing cushioning? Hans has confirmed that propellant is brought back regardless (though see point below).

3. "In the event of an abort, a water landing is highly likely, so might as well do water landings across the board". Not sure this logic holds either - as in, the same could be said for Starliner, yet Boeing nominally does land landings. One consideration is that in an abort that also ends in a land landing, is there prop margin available for the micro firing of the superdracos.

What's missing? I would think, if there's not a relatively huge amount of development to implement it, that land landings is a much more effectual way to go when the intention is to ultimately reuse the D2.

I relabeled them 1,2,3 for ease of reference.
1 & 2 are not the reason.
3 IS the reason, but the statement that Boeing opted for land landing for caparison is misleading.
Both SpaceX and Boeing opted for land landing. NASA did not nix land landing. It nixed propulsive landing, so the Boeing comparison is apples to oranges.
Water landing was already the secondary option so SpaceX simply made it the primary in order to meet the contract operational date requirements.

Emphasis mine.

Correct.
The land-landing method chosen by SpaceX was propulsive landing. First of all because it is what Elon originally intended. Second: it had the potential of rapidly re-using the capsule with minimal refurbishment.

By the time NASA threw a wrench in the propulsive landing scenario SpaceX still had plans to reuse flown Crew Dragons for secondary missions (such as tourist flights and unmanned LEO scientific mission akin to the original Dragon Lab plans). These plans included reuse of the primary heatshield.

Doing non-propulsive land-landing (in other words: parachutes) would have required a cushioning system to soften the impact of landing. Most solutions for that require the primary heatshield (which, by the way, is rather expensive) to be dumped before landing. Much like Starliner and Soyuz are doing. That in turn requires installation of a new primary heatshield before re-flight (like is done on re-flights of cargo Dragon).

The alternative was to land Crew Dragon in the ocean (like is already done with cargo Dragon). For re-flight that would require corrosion prevention and refurbishment activities (also expensive) similar to those done for re-flight of cargo Dragon.

Both scenarios preclude rapid reuse, minimal refurbishment re-flights of Crew Dragon. Faced with this "dilemma" SpaceX chose to stick with the basic design of Crew Dragon and promote the backup landing method (parachutes) to become the primary landing method. As well as letting go of any plans for rapid reuse, minimal refurbishment re-flights of Crew Dragon.

[geza]

Giving up powered landing of Dragon was porbably related also to the changing Mars plans. As Elon stressed many times, powered landing could be used anywehere, esp. on Moon and Mars. Supersonic retropropulsion with SuperDracos was the way of landing for Red Dragon. Speculations about BFR/MCT before the lecture by Elon in 2016 usually assumed that the upper stage would be like a large Dragon. I don't know, if we have any confirmation on such plans internally in SX. Certainly, the '16 lecture presented an EDL concept very different from the Dragon one.

So, my speculation is that Elon lost his interest in landing Dragon via SuperDracos partially, because it had become clear that it would not be the precursor of the future spacecraft. Now Dragon is seen as an interim solution, which will be replaced by Starship ASAP.

[clongton]

So many people like to get all googly-eyed at the latest, biggest, baddest heavy lift LV and spacecraft. In the discussion of Dragon vs. Starship, there is room for both. I like to look at the aircraft industry for a real-world comparison.

There may be 10s of thousands of larger passenger and cargo carrying aircraft, carrying millions of tons of cargo and millions of passengers all around the world annually. But there are millions of smaller, lighter, more limited aircraft as well, carrying less cargo and fewer passengers with each flight. Nobody would suggest that smaller airplanes should go away because now we have bigger Boeing and Airbus giants in the skies. I think the same should apply to spacecraft. I firmly believe that there is a market for smaller spacecraft something like Dragon or Starliner, for either LEO destinations or P2P flights. But the trick is going to be the launch cost. Bring down the launch costs for smaller spacecraft, ala SpaceX reusability, and that market will take off, and propulsive landing will need to be the standard EDL procedure, not parachutes. For example, I can easily see a reusable Falcon 9 core stage with no disposable upper stage executing a P2P flight for the Dragon. The core stage retrofires and returns to the launch site and the Dragon continues to it's destination way,

As SpaceX advances Starship into an operational vehicle, I truly hope they do not abandon the small craft industry to others. That would be a huge mistake imo.

[clongton]

So many people like to get all googly-eyed at the latest, biggest, baddest heavy lift LV and spacecraft. In the discussion of Dragon vs. Starship, there is room for both. I like to look at the aircraft industry for a real-world comparison.

There may be 10s of thousands of larger passenger and cargo carrying aircraft, carrying millions of tons of cargo and millions of passengers all around the world annually. But there are millions of smaller, lighter, more limited aircraft as well, carrying less cargo and fewer passengers with each flight. Nobody would suggest that smaller airplanes should go away because now we have bigger Boeing and Airbus giants in the skies. I think the same should apply to spacecraft. I firmly believe that there is a market for smaller spacecraft something like Dragon or Starliner, for either LEO destinations or P2P flights. But the trick is going to be the launch cost. Bring down the launch costs for smaller spacecraft, ala SpaceX reusability, and that market will take off, and propulsive landing will need to be the standard EDL procedure, not parachutes. For example, I can easily see a reusable Falcon 9 core stage with no disposable upper stage executing a P2P flight for the Dragon. The core stage retrofires and returns to the launch site and the Dragon continues to it's destination way, way downrange somewhere, carrying 4-5 people or cargo, faster than any other possible method. Question for those of you with the software capability to do so: could a Falcon-9 core stage lob a Dragon Spacecraft across the Atlantic if the trajectory was designed for P2P instead of LEO?

I used Falcon-9 and Dragon as an example only, not necessarily as the actual vehicles, just to make the point. But as SpaceX advances Starship into an operational vehicle, I truly hope they do not abandon the small craft industry to others. That would be a huge mistake imo.

[woods170]

So many people like to get all googly-eyed at the latest, biggest, baddest heavy lift LV and spacecraft. In the discussion of Dragon vs. Starship, there is room for both. I like to look at the aircraft industry for a real-world comparison.

There may be 10s of thousands of larger passenger and cargo carrying aircraft, carrying millions of tons of cargo and millions of passengers all around the world annually. But there are millions of smaller, lighter, more limited aircraft as well, carrying less cargo and fewer passengers with each flight. Nobody would suggest that smaller airplanes should go away because now we have bigger Boeing and Airbus giants in the skies. I think the same should apply to spacecraft. I firmly believe that there is a market for smaller spacecraft something like Dragon or Starliner, for either LEO destinations or P2P flights. But the trick is going to be the launch cost. Bring down the launch costs for smaller spacecraft, ala SpaceX reusability, and that market will take off, and propulsive landing will need to be the standard EDL procedure, not parachutes. For example, I can easily see a reusable Falcon 9 core stage with no disposable upper stage executing a P2P flight for the Dragon. The core stage retrofires and returns to the launch site and the Dragon continues to it's destination way,

As SpaceX advances Starship into an operational vehicle, I truly hope they do not abandon the small craft industry to others. That would be a huge mistake imo.

Other than NASA there are no customers for the smaller craft. Same applies to cargo Dragon. It is the very reason why the Dragon Lab initiative quietly faded into oblivion.

Like it or not but all bets are on Superheavy and Starship. Crew Dragon will soldier on for the duration of ISS, after which it will also quietly go away IMO. F9 and FH will probably last a little longer but they also will eventually be retired. Remember: SpaceX is a very agile company. And those tend to do away with "old" stuff fairly quickly.

[Tulse]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one. Musk has repeatedly said that Starship will be cheaper to launch than Falcon -- not just cheaper per payload kilo, but cheaper overall. I think it will be very hard for a smaller vehicle to beat Starship pricing. And unless a payload needs to be delivered on its own at a highly specific time (e.g., some national security sats), regularly scheduled rideshares will allow any sized payload to be delivered by Starship.  Once Starship is in regular service, it's very possible that the market for dedicated smaller launchers will be greatly reduced.

[FutureSpaceTourist]

https://twitter.com/jimbridenstine/status/1218244543209852928

Suited up! While crew members won't be aboard #CrewDragon during tomorrow's @SpaceX In-Flight Abort Test, astronauts Bob Behnken & Doug Hurley rehearsed what they'll experience during @Commercial_Crew missions. I'm excited we'll soon launch American astronauts from American soil!

[geza]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.

Why is this, exactly?

[joncz]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.

Why is this, exactly?

Surface area and volume increase faster than mass.  A larger stage is "fluffier"

[rsdavis9]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.

Why is this, exactly?

Mass fractions.
Look at the total takeoff weight of SH/SS and it can deliver 100t to orbit.
Reuseability always affects performance.
SH 3500t
SS 2900t
total 6400t
100t/6400t=.015
Whats the ratio for falcon9?

EDIT:
falcon9
549t
23t
23/549=.041

both from wikipedia

EDIT: EDIT:

Put another way if you want to have full reuse and get the same mass to orbit you need a bigger rocket.

[su27k]

I used Falcon-9 and Dragon as an example only, not necessarily as the actual vehicles, just to make the point. But as SpaceX advances Starship into an operational vehicle, I truly hope they do not abandon the small craft industry to others. That would be a huge mistake imo.

They will abandon the small spacecraft industry to others, just like they abandoned small launcher industry to others. SpaceX is taking on two multi-billion dollar projects (Starship and Starlink), they cannot afford to be distracted, they need to focus everything they have on these two projects.

Besides, if you use aircraft industry as analog, yes there're large plane manufacturers and small plane manufacturers, but they're usually not the same company, i.e. Boeing builds 787s while Textron builds Cessna, both are on the Fortune 500 list. A robust space economy would allow both big spacecraft and small spacecraft manufacturers to flourish.

[clongton]

Besides, if you use aircraft industry as analog, yes there're large plane manufacturers and small plane manufacturers, but they're usually not the same company ...

Point well taken.

[livingjw]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.

Why is this, exactly?

Surface area and volume increase faster than mass.  A larger stage is "fluffier"

This is wrong:

- Volume is close to linearly proportional to vehicle mass. This is due, primarily  to tanks and engines being proportional to mass.

- Surface area increases slower than volume. Area is proportional to volume to the 2/3rds power for the same shape. If you want to maintain a constant Ballistic Coefficient, BC, then Area will be nearer to being proportional mass as well.

- Bottom line, for a reusable rocket constrained by reentry BC, not much changes with gross weight.

John

[geza]

As I understand it, it is a lot easier (and thus cheaper) to make a larger second stage reusable than a smaller one.

Why is this, exactly?

Surface area and volume increase faster than mass.  A larger stage is "fluffier"

This is wrong:

- Volume is close to linearly proportional to vehicle mass. This is due, primarily  to tanks and engines being proportional to mass.

- Surface area increases slower than volume. Area is proportional to volume to the 2/3rds power for the same shape. If you want to maintain a constant Ballistic Coefficient, BC, then Area will be nearer to being proportional mass as well.

- Bottom line, for a reusable rocket constrained by reentry BC, not much changes with gross weight.

John

John, I understand only the first half of what you wrote. Volume and mass scale together but surface increases slower. It implies that BC (mass/area) increases with increasing gross weigth. That is EDL is more difficult for larger spacecrafts. If I understand correctly, this is why it is non-trivial to scale-up the existing Martian EDL systems. This is why huge deployable heat shildes are often proposed for large Mars landers. And this is why Starship entry is sideways.

This is why I do not understand, why people assume full resuability being easier for larger rockets.

[blasphemer]

There is a point where your rocket is simply too small to even achieve orbit, much less have any margin for reusability. So simply increasing rocket size can be beneficial by itself, increasing payload fraction and/or delta-v. Probably some square-cube law. Not sure how far this relationship extends, but I wouldn't be surprised if this results in some really huge reusable launch systems in the future.