Author Topic: Does SpaceX have any launch scrub scenario's due to bad landing conditions?  (Read 3995 times)

Offline MoDyna

With the importance to SpaceX to recover their F9 boosters and the bad sea state and wind shear that made today's landing iffy, I was wondering if SpaceX has developed launch scrub conditions where the launch conditions are within criteria, but the landing conditions are not. If so, do you think that today's landing gave them enough information to develop some or are they just prepared to lose the booster?

Offline Kabloona

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SpaceX started publishing "landing commit criteria" similar to "launch commit criteria" over 3 years ago.

https://forum.nasaspaceflight.com/index.php?topic=36326.msg1357592#msg1357592

I don't remember if there have been any outright scrubs for downrange weather, but there was at least one delay (Flight 20) that SpaceX attributed to both a technical problem on the vehicle (LOX subcooling) and downrange weather.

The criteria numbers may have changed since then, but it's still conceivable there will be times when conditions at the launch site are within limits and conditions for recovery at sea are not.

Given SpaceX's financial interest in recovering as many F9's as possible, it seems to me they would write their launch contracts to include language that allows them to scrub for such cases without penalty. After all, the non-expendable customers are getting a price break, and allowing SpaceX to scrub for conditions downrange is a reasonable concession for the lower price.

« Last Edit: 07/25/2018 10:18 pm by Kabloona »

Offline ehb

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They were willing to risk it today ;)

Perhaps when they have a fleet of multiply reused F9s and sufficient data on landings in various conditions to do a sound risk assessment, they will be more proactive on this issue.  Extending Kabloona's speculation, they could then include an optional contract cost item to launch regardless of downrange conditions for customers with time critical payloads.

Offline Lar

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I predict that within a year or two we will see SpaceX do at least one scrub for  weather that is recovery criteria (not launch criteria) related. They would be foolish not to start writing all their contracts this way.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline archae86

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Learning and availability both issues
« Reply #4 on: 07/25/2018 11:29 pm »
At this stage it might make sense for them not to have graven in stone fixed criteria thought to be zero risk.

I seriously doubt they really know a full description of boundary-line conditions for success.  Quite possibly some opportunities to observe actual vehicle dynamics in marginal conditions might improve their ability to delineate the success threshold.  It might also allow for further improvement--most likely in code--based on better understanding.  This consideration might motivate them to attempt a flight for which current conditions are believed to pose appreciable landing risk.

Another issue that would make sense to consider would be the near-term availability of first stages.  If they have fallen behind critical customer needs, it may make sense to use tighter criteria, reflecting the greater opportunity cost compared to a time of abundant supply.

Online John Alan

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Some ASDS landings of the distant past have had some hair raising video (post landing) with whitecaps and the ASDS pitching and bucking...  :o
One IIRC came in leaning hard into a stiff wind and righted itself at the last second...  8)
I honestly think they would even trying landing S1 on ASDS in a local rain shower (not a thunderstorm)...  ;)

That said... the faring's are not near as forgiving to weather (it seems), and they MAY become the leading issue to scrub a launch someday (down the road)... Once that is sorted out...

 ;)

Offline Spudley

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I predict that at some point, SpaceX's recoveries are going to become so routine that they (or more likely their clients) will be able to purchase a reasonably priced insurance that covers the possibility of them losing the booster (or fairings, or whatever else) regardless of weather conditions.

As a client, if you pay for this insurance, then you would basically be paying for an assurance that SpaceX will not scrub your launch due to downrange weather. SpaceX would still try to catch the booster, but would be covered if they failed to.

Online M.E.T.

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This question seems very significant for BFS landings with humans on board - particularly on return trips from Mars. If the BFS does not have enough fuel to slow down into Earth orbit, does that mean that it has to enter the atmosphere and land at the moment of arrival, irrespective of weather conditions at the landing site?

That sounds a bit problematic, for obvious reasons.
« Last Edit: 07/29/2018 12:11 am by M.E.T. »

Offline archae86

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Alternates
« Reply #8 on: 07/29/2018 02:51 pm »
does that mean that it has to enter the atmosphere and land at the moment of arrival, irrespective of weather conditions at the landing site
There is a related problem in long-range commercial aviation.  They can't confidently know that weather (or even runway availability) at the intended destination will permit landing on arrival, and they don't have nearly enough spare fuel to just circle until things get better for a significant fraction of cases.  The accepted solution in that aviation is alternate landing sites, all reachable on original trip fuel (though not necessarily reachable if the decision is made too late).

I'll wager Mars operations will entail _not_ orbiting Earth on return, but will include at least one alternate landing site, maybe more.  Holding down excess fuel requirement would mean making the divert decision a ways out.

Offline guckyfan

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Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.

Online M.E.T.

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Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.

In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry.

Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?

Offline lucas071200

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How deep would you have to dive into atmosphere for going into high elliptical orbit with aerobraking ?

Offline guckyfan

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Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.

In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry.

Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?

They won't have anywhere near enough propellant for propulsive braking. They still need to shed the interplanetary speed with the heat shield and do a perigee raising burn to stay in orbit.

I don't know enough about trajectories. Maybe they could brake into EML-1 or 2 with little propellant as an emergency measure. But that would be very inconvenient for efficient normal operation. Would probably only work on a slow Hohmann transfer. SpaceX wants faster trajectories.

Offline envy887

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Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.

In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry.

Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?

They won't have anywhere near enough propellant for propulsive braking. They still need to shed the interplanetary speed with the heat shield and do a perigee raising burn to stay in orbit.

I don't know enough about trajectories. Maybe they could brake into EML-1 or 2 with little propellant as an emergency measure. But that would be very inconvenient for efficient normal operation. Would probably only work on a slow Hohmann transfer. SpaceX wants faster trajectories.

That depends on the speed of the return. For a slower return the fuel needed to brake into an Earth orbit with a very high apogee should be less than required for landing. This would also work for a high speed return with a smaller payload.

Or a lunar flyby could also shed up to 1 km/s and result in a completely passive capture without ever entering the atmosphere.

Or you could do the heat shield inspection just before reaching Earth. The MMOD risk in interplanetary space is extremely low.

Offline alexterrell

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Changing landing sites may not be easy or possible with a late decision. The time and direction of arrival are pretty much fixed. Braking into orbit and then refueling may be a real possibility.

In fact, braking into orbit may be preferable for many reasons. Including doing a thorough inspection of the state of the heatshield prior to re-entry.

Does BFS carry sufficient fuel upon a Mars return journey to brake into Earth orbit?
Breaking into orbit - from Mars - dissipates about half as much heat as a landing (about 25MJ/kg). So a heat shield inspection might need to be done earlier - ideally in Mars orbit.

That said, splitting the "heat shield operation" into two easier manoeuvres might make sense.
« Last Edit: 09/07/2018 07:02 pm by alexterrell »

Offline alexterrell

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Some criteria will make sense, and they may already have them

However, these are driven by "Probability of launch success" where they will be aiming to maximise this. They may decide they only need a probability of 95% for landing capture.

If the weather is lousy at the landing sight, will it be OK at the launch site?

The other criteria is launch window. If it's a small and rare window, they mighthave to rish the recovery. If the window repeats every day, delaying the launch by a day might e cheaper than the risk of losing a booster.
« Last Edit: 09/07/2018 07:06 pm by alexterrell »

Offline speedevil

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How deep would you have to dive into atmosphere for going into high elliptical orbit with aerobraking ?

There are several answers to 'abort to near earth', not actually land.

One pass 'hard' aerocapture - on the order of 80km or so - broadly at the point in the entry where you would normally continue vectoring the aerodynamic lift into keeping you in the atmosphere at supersynchronus speeds (8.5)km/s or so, you spin 180, and use it to bounce you back out.
This needs only a tiny amount of circularisation, but is very heavy thermally.

A much shallower pass, ending up at 11km/s and and ending up in a bound very eccentric orbit, where you can slowly aerobrake down to LEO. (this has multiple magnetic field encounters so may be bad for crew).

Entirely propulsive matching, of around a kilometer a second again, ending up in an eccentric orbit. This can be combined with gentle aerobraking not requiring any TPS. Gentle aerobraking means multiple radiation belt passes.

Adding recovery craft increases options a lot.



Offline TripleSeven

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Re: Alternates
« Reply #17 on: 09/07/2018 09:58 pm »
does that mean that it has to enter the atmosphere and land at the moment of arrival, irrespective of weather conditions at the landing site
There is a related problem in long-range commercial aviation.  They can't confidently know that weather (or even runway availability) at the intended destination will permit landing on arrival, and they don't have nearly enough spare fuel to just circle until things get better for a significant fraction of cases.  The accepted solution in that aviation is alternate landing sites, all reachable on original trip fuel (though not necessarily reachable if the decision is made too late).

I'll wager Mars operations will entail _not_ orbiting Earth on return, but will include at least one alternate landing site, maybe more.  Holding down excess fuel requirement would mean making the divert decision a ways out.

as we say here "tabbi tabbi" kind of but...

the rules governing fuel at destination in terms of alternate AND weather are clearly laid out and are done so all in terms of runway and approach availability.

for instance the amount of fuel carried changes enormously if the destination airport has only 1 runway and 1 precision approach system (precision approachs  on each end of the runway dont count)..

If there are two runways (not intersecting) and two precision approaches what does change some of the fuel can be offloaded and  the ability to ignore when the airplane has reached alt fuel meaning one has to go to the alternate....and then some very specific rules click into affect for what is called "commitment to stay"

what this "more or less" means is that on our worst long haul route (which is Istanbul to LAX) we arrive at LAX with over 1 hour of fuel that we can 'burn" before considering  the alternate.  We could "commit to stay" because LAX has 2 (or more) runways but that is completely a Captains decision.    We can orbit for  "more than 1 hour" if say Ontario can be used for the alt.  if it cannot (but it mostly can LAX problem is generally fog) Ontario will give us at least that "one hour" (my experience is about an hour and 40 minutes)

If we 1) dont have adequate forecast...we cannot go.  or 2) cannot find an alternate airport to go to ONCE we have gotten to the airport of destination (this is called isolated airport and I cannot think of one we fly to that meets that requirement...but an example is the South POle landing strip :) ) then we have to tanker nearly 3 hours of fuel. (that is why I cannot think of an airport....3 hours is 1/4 the trip to LAX :)

the rules are in the process of changing a bit due to performance based navigation

the big deal now is that the Triple 7 can autoland (ie land in zero zero visibility) if the runway landing system has that capability (CAT IIIB) BUT the weather forecast right now...are always downgraded by 1 capability.  So for instance if the airplane is CATIII we must assume weather no worse than CAT II at the alternate or we need more fuel.

with PBN the airplane no longer cares about the ground systems...and with double redundant airplane based landing systems, the regulators are looking at changing the requirement to down grade.

the weather forecast are 1) very good and 2) now the plane gets updates as fast as they are published...and if they go down, that will change the dispatch fuel.

the decision can never be made to "late" when the FMS says "ALT FUEL" if you cannot commit to stay...then by law you have to go.  If you dont look like you are going quickly, dispatch will call you quickly :) but in all cases if you go when "ALT FUEL" comes on...you will, if you go straight to your destination as an "ALT FUEL" airplane land with at least 1:15 minutes of fuel left...45 minutes of hold time and 30 minutes emergency.

Alt Fuel is completely apart from what is called "Trip fuel" 

the worst case I have ever had...was Istanbul to Manila.  we had two hours 15 minutes of hold fuel when I got into the hold.  I used an hour and 45 minutes of it.  Dodging typhoon squalls.  In four years at my present job I have diverted 1 time.  Gatwick ..American Airlines B767 landed in front of me and blew all his tires...off to Heathrow :) in nearly 30,000 hours I have diverted 3 times including that one.

« Last Edit: 09/07/2018 10:04 pm by TripleSeven »

Offline Lar

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Relevance?

The airplane analogy was an analogy, nothing more. A really long and detailed explanation of aircraft landing procedures without drawing parallels is of no value other than letting you brag about how much you know about your job. Take it to an aviation forum.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

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