Gwynne Shotwell lecture at Stanford 11 Oct 2017

[Lar]

Of course, for large cargo payloads you can just land on 2.

not redundantly if it only has 2.

[RocketmanUS]

Rewatched the presentation, linked from SpaceX website. What Elon said was 20 to 50 t returnable from Mars by the BFS with no booster ( or no LMO refueling , implied ), this is at 35:21.

What I asked was what the BFS is capable of landing back on Earth. I did not ask from were the BFS was coming from as it did not matter. What does matter is what the BFS structure can handle on landing. Space shuttle was designed to launch up to 65.000 lb, later revised to launching maximum 50,000 lb. However space shuttle could only land with 35,000 lb of cargo, just like commercial jets can not land with full tanks , the structure can not handle it. Important to know if there is a sub orbital abort or an orbital abort.

The limitation is not structural. For redundacy, the ship needs to be able to land on a single Raptor SL, which has about 170mT of thrust. If the ship is 85mT, and landing propellant is another 35mT, then 50mT is the maximum payload.

Thanks.
With a 719 m/s delta v for landing with one engine only that would be correct ( just ran the numbers ). With two of the sea level engines it could land with 150 t, but could the structure handle it?

Could they use one or two vacuum engines with one sea level engine to land? Or would the vacuum engines not work at sea level on landing on Earth.

[Robotbeat]

Of course, for large cargo payloads you can just land on 2.

not redundantly if it only has 2.

That's why I said cargo.

[kdhilliard]

Rewatched the presentation, linked from SpaceX website. What Elon said was 20 to 50 t returnable from Mars by the BFS with no booster ( or no LMO refueling , implied ), this is at 35:21.

What I asked was what the BFS is capable of landing back on Earth.
...

At 17:00 he discusses the BFS specs and says, "And that ship will contain 1,100 tons propellant with an ascent design of 150 tons and return mass of 50."  The side shown at that time says, "Max Ascent Payload 150 t / Typical Return Payload 50 t".  He does not explain the limiting factor. (Transcript)

~Kirk

[RocketmanUS]

Rewatched the presentation, linked from SpaceX website. What Elon said was 20 to 50 t returnable from Mars by the BFS with no booster ( or no LMO refueling , implied ), this is at 35:21.

What I asked was what the BFS is capable of landing back on Earth.
...

At 17:00 he discusses the BFS specs and says, "And that ship will contain 1,100 tons propellant with an ascent design of 150 tons and return mass of 50."  The side shown at that time says, "Max Ascent Payload 150 t / Typical Return Payload 50 t".  He does not explain the limiting factor. (Transcript)

~Kirk

Thanks.
OneSpeed explained it do to engine out.
That limits the point to point to 50 t for crew safety minus unusable propellants.

I still would have liked to know the structural limit on BFS for payload on landing on Earth, ( for Chomper and crew/cargo versions )

[Lars-J]

Of course, for large cargo payloads you can just land on 2.

not redundantly if it only has 2.

That's why I said cargo.

That's using an 'expendable' mindset. They are going to try to reuse these potentially hundreds of time, it is IRRELEVANT whether or not there are people on board.

Does a cargo aircraft push their specs beyond safety margins, just because it carries cargo? No... The aircraft is far more valuable than the cargo.

The safety margins will be essential for the BFS, if for no other reason that it needs to prove the highest amount of reliability. If a BFS craters on landing, people aren't going to say that "it was only cargo" and pretend nothing happened.

[deruch]

Derek F.

Now that your job is much more business related, what part of the day-to-day, hands-on engineering you did earlier in your career do you miss the most/least?


By the way, Helodriver is totally crushing that list.

[speedevil]

That's using an 'expendable' mindset. They are going to try to reuse these potentially hundreds of time, it is IRRELEVANT whether or not there are people on board.

Does a cargo aircraft push their specs beyond safety margins, just because it carries cargo? No... The aircraft is far more valuable than the cargo.

The safety margins will be essential for the BFS, if for no other reason that it needs to prove the highest amount of reliability. If a BFS craters on landing, people aren't going to say that "it was only cargo" and pretend nothing happened.

Only for 'political' reasons.
Airliner reliability is of the order of one death in ten million journeys. (for a given passenger).

Assuming for the moment BFR gets to airliner like reliability on two engines, and this is the only risk involved, that is one chance in ten million of both engines failing, or one chance in 3000 of one engine failing.
For a $300M BFS failing, that's of the order of $100K cost.

That is considerably less than the cost of one BFR launch.


An

[abaddon]

The safety margins will be essential for the BFS, if for no other reason that it needs to prove the highest amount of reliability. If a BFS craters on landing, people aren't going to say that "it was only cargo" and pretend nothing happened.

Agreed.  Not to mention, these things are going to be expensive.

The margin might very well be based on single engine out margin - that makes sense - but they may also design the structural loads based around that assumption, so it could end up being both.

[TrueBlueWitt]

Which vehicle(s) will SpaceX put forward in response to the new AF request?

[leetdan]

Since current F9 cores are only good for a single reuse, what is the business case for recovering the cores on their terminal flight?

[hkultala]

Since current F9 cores are only good for a single reuse, what is the business case for recovering the cores on their terminal flight?

There is no such limitation.

[mikes]

Since current F9 cores are only good for a single reuse, what is the business case for recovering the cores on their terminal flight?

There is no such limitation.

Even if there were:

* post-flight inspection to check component performance and look for potential problems

* practice

[ejb749]

Will there be a webcast of the event? 
Does she know there is a launch scheduled for the exact same time?

[leetdan]

There is no such limitation.

My mistake, I thought this had been explicitly stated somewhere.  It seems implied from the lack of reuse of GTO cores to date.

Engineering analysis is an obvious benefit, but each would tend to reveal less as more cores return for inspection.  Checking out operational changes like the Octagrabber are also evident.  Maybe I should've explicitly asked if any flight hardware has the potential for reuse even if the core as a whole is retired.

[meberbs]

Does she know there is a launch scheduled for the exact same time?

Since there is not a launch scheduled at the same time (it is 3 hours before with a 2 hour window, and should be less than 1 hour to payload deploy from launch), I believe the answer is "no."

(Check your timezones, Stanford is in CA.)

[RocketmanUS]

The safety margins will be essential for the BFS, if for no other reason that it needs to prove the highest amount of reliability. If a BFS craters on landing, people aren't going to say that "it was only cargo" and pretend nothing happened.

Agreed.  Not to mention, these things are going to be expensive.

The margin might very well be based on single engine out margin - that makes sense - but they may also design the structural loads based around that assumption, so it could end up being both.

One of the reasons is abort back to Earth. If there is an issue with BFS after booster separation before getting to orbit it would need to land back on Earth. But could the structure handle landing with some of the propellant mass that was not used that would have been used to get to orbit.  The BFS might be able to use the vacuum engines for extra thrust if needed for landing. This would be a BFS with crew.

[neoforce]

Since it is hosted by Stanford Student Space Initiative, I doubt there will be a live steam. I will anxiously await hellodrivers report after the fact.   https://stanfordssi.org/blog/gwynne-shotwell-road-to-mars

Another interesting tidbit from the website for the talk:  "Q&A session hosted by Steve Jurvetson."  So for those lucky enough to be in attendance you get two powerhouse personalities in the room.

[jpo234]

I will anxiously await hellodrivers report after the fact.

It's helodriver, as in helicopter driver.

[Robotbeat]

Of course, for large cargo payloads you can just land on 2.

not redundantly if it only has 2.

That's why I said cargo.

That's using an 'expendable' mindset. They are going to try to reuse these potentially hundreds of time, it is IRRELEVANT whether or not there are people on board.

Does a cargo aircraft push their specs beyond safety margins, just because it carries cargo? No... The aircraft is far more valuable than the cargo.

The safety margins will be essential for the BFS, if for no other reason that it needs to prove the highest amount of reliability. If a BFS craters on landing, people aren't going to say that "it was only cargo" and pretend nothing happened.

*sigh*
This is tiresome. This is not "expendable mindset."

The context was "what is the maximum landing payload?" I answered that.

Whether they wish to utilize that capability is up to them, but your SPECULATION that SpaceX would be too afraid (Are we talking about the same company???) of public perception of failed landings is off-topic to the question at hand. Additionally, BFR will necessarily be incredibly safe even without engine-out capability.