Author Topic: First stage rocket hop back to the launch site  (Read 4912 times)

Offline jee_c2

  • Member
  • Posts: 83
  • Budapest, Hungary
  • Liked: 7
  • Likes Given: 8
First stage rocket hop back to the launch site
« on: 08/17/2018 09:10 am »
After the first stage landed somewhere else, not on the launch site, i.e. on a sea platform, would it be meaningful to consider a rocket powered hop flight back to the launch site?

It would require
- a refill (only small amount of fuel is needed!),
- an in situ quick inspection of the stage
- a new flight software for flying back to the launch site (or wherever it should go). /I'm not sure, may be the current is good enough to handle this task as well)

Benefits:
- transport time way less
- no other, usual transport costs (resources)

Drawbacks:
- one more flight, even if it is only a "hop"
- more usage of the thrusters, rocket engines
- additional risks

Are there such plans?
It is obvoius, the more robust the first stage (block 5 is the best  until now), the more sense to do it.
What is your opinion?

(I looked around, but haven't found discussion about this, if there is one somewhere still, I'm sorry, and please give me a link to the topic.)

Offline Beittil

Re: First stage rocket hop back to the launch site
« Reply #1 on: 08/17/2018 09:25 am »
A couple of deployed landing legs alone would make this highly improbable and impractical I think. As we have seen they need that new hood cap and a wire pulling system to restow the legs for flight, how would you go about that on the ASDS? I don't think lifting off with the legs deployed is highly recommendable :D

Offline octavo

  • Full Member
  • *
  • Posts: 135
  • Liked: 72
  • Likes Given: 201
Re: First stage rocket hop back to the launch site
« Reply #2 on: 08/17/2018 09:48 am »
After the first stage landed somewhere else, not on the launch site, i.e. on a sea platform, would it be meaningful to consider a rocket powered hop flight back to the launch site?

It would require
- a refill (only small amount of fuel is needed!),
- an in situ quick inspection of the stage
- a new flight software for flying back to the launch site (or wherever it should go). /I'm not sure, may be the current is good enough to handle this task as well)

Benefits:
- transport time way less
- no other, usual transport costs (resources)

Drawbacks:
- one more flight, even if it is only a "hop"
- more usage of the thrusters, rocket engines
- additional risks

Are there such plans?
It is obvoius, the more robust the first stage (block 5 is the best  until now), the more sense to do it.
What is your opinion?

(I looked around, but haven't found discussion about this, if there is one somewhere still, I'm sorry, and please give me a link to the topic.)

Musk bruited the idea early on I believe, but it does not seem like any serious work has been done on the concept. It looks very much like SpX would rather roll efficiencies like this into BFR, rather than invest in that tech for F9.

Cradle landings for the BFR point in this direction.

The investment required to get this working on F9 would not be insignificant. Your ASDS now needs to carry RP1, LOX + a chiller to subcool the LOX, TEA-TEB tanks to refill the ignition system, a launch mount, some sort of flame trench/deflector and none of that addresses the point that F9 first stage is not designed to fly upwards with an open interstage. The aerodynamic modelling would have be done for this as well.

Offline jee_c2

  • Member
  • Posts: 83
  • Budapest, Hungary
  • Liked: 7
  • Likes Given: 8
Re: First stage rocket hop back to the launch site
« Reply #3 on: 08/17/2018 09:48 am »
A couple of deployed landing legs alone would make this highly improbable and impractical I think. As we have seen they need that new hood cap and a wire pulling system to restow the legs for flight, how would you go about that on the ASDS? I don't think lifting off with the legs deployed is highly recommendable :D
You are right, the landing legs are a problem currently.

If the legs would be moved back to it's starting/flying position, something should keep the first stage standing, so it could be launched again. Sounds problematic.
Improving the first stage to allow the legs to be pulled back would be better, but that is of course weight penalty, and new design. So this is another drawback.

Offline envy887

  • Senior Member
  • *****
  • Posts: 5206
  • Liked: 3094
  • Likes Given: 1554
Re: First stage rocket hop back to the launch site
« Reply #4 on: 08/17/2018 12:50 pm »
F9 would be at best unstable and at worst structurally unable to fly at the required speeds with the interstage open. It would probably need a nose cone, and some way of attaching it to the top of the rocket out in the middle of the ocean.

And some portable launch mount and flame deflector would be needed. Crew would have to roll out the launch mount under the booster, jack it up, hook up the fluids connections (starter fluid, LOX/RP-1, helium, nitrogen), fold up the legs, install the nose cone, and then retreat to the support ship for load and launch.

Is it possible? Sure. Is it worth the effort, instead of building another ASDS? Apparently not, since SpaceX is instead building another ASDS.

Offline Celestar

  • Member
  • Posts: 16
  • Liked: 13
  • Likes Given: 1
Re: First stage rocket hop back to the launch site
« Reply #5 on: 08/17/2018 01:56 pm »
Slightly OT, but could one not load the stage horizontally onto a different (i. e. faster) vessel and just leave the ASDS out at sea for a couple of launches?

Celestar

Sent from my G8441 using Tapatalk


Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 1113
  • Liked: 462
  • Likes Given: 405
Re: First stage rocket hop back to the launch site
« Reply #6 on: 08/17/2018 02:19 pm »
SeaLaunch Commander would be ideal for this...

Offline jee_c2

  • Member
  • Posts: 83
  • Budapest, Hungary
  • Liked: 7
  • Likes Given: 8
Re: First stage rocket hop back to the launch site
« Reply #7 on: 08/17/2018 06:49 pm »
F9 would be at best unstable and at worst structurally unable to fly at the required speeds with the interstage open. It would probably need a nose cone, and some way of attaching it to the top of the rocket out in the middle of the ocean.

And some portable launch mount and flame deflector would be needed. Crew would have to roll out the launch mount under the booster, jack it up, hook up the fluids connections (starter fluid, LOX/RP-1, helium, nitrogen), fold up the legs, install the nose cone, and then retreat to the support ship for load and launch.

Is it possible? Sure. Is it worth the effort, instead of building another ASDS? Apparently not, since SpaceX is instead building another ASDS.
Well summed, thanks all for collecting the needs for this home-hop method. So, most probably, not worth it. Just for some mind practice, I have some thoughts about it.

I don't know exactly how much ground transport is needed beside the ASDS, but that also would be eliminated by the hop.

About the aerodynamic load: some sort of nose cone is necessary for sure.
Could it be attached the same way, as the second stage is connected?
How would the flight profil look like for the return trp? Perhaps optimized for low aerodynamic pressure? Fuel would not be that much of a problem.

Offline Ludus

  • Full Member
  • ****
  • Posts: 1215
  • Liked: 621
  • Likes Given: 308
Re: First stage rocket hop back to the launch site
« Reply #8 on: 09/16/2018 04:12 am »
F9 would be at best unstable and at worst structurally unable to fly at the required speeds with the interstage open. It would probably need a nose cone, and some way of attaching it to the top of the rocket out in the middle of the ocean.

And some portable launch mount and flame deflector would be needed. Crew would have to roll out the launch mount under the booster, jack it up, hook up the fluids connections (starter fluid, LOX/RP-1, helium, nitrogen), fold up the legs, install the nose cone, and then retreat to the support ship for load and launch.

Is it possible? Sure. Is it worth the effort, instead of building another ASDS? Apparently not, since SpaceX is instead building another ASDS.
Well summed, thanks all for collecting the needs for this home-hop method. So, most probably, not worth it. Just for some mind practice, I have some thoughts about it.

I don't know exactly how much ground transport is needed beside the ASDS, but that also would be eliminated by the hop.

About the aerodynamic load: some sort of nose cone is necessary for sure.
Could it be attached the same way, as the second stage is connected?
How would the flight profil look like for the return trp? Perhaps optimized for low aerodynamic pressure? Fuel would not be that much of a problem.

Although it doesn’t seem worth it for F9, SpaceX seems to be rolling this into BFR/BFS. BFS seems fully capable of landing somewhere to deliver passengers or cargo that has only limited propellant loading capacity then taking off again for a short hop of a few hundred or thousand miles to get back to a major spaceport that can launch it on top of a BFR booster. Hop back to a launch site.

Offline vanoord

  • Full Member
  • ****
  • Posts: 636
  • Liked: 377
  • Likes Given: 78
Re: First stage rocket hop back to the launch site
« Reply #9 on: 09/16/2018 09:32 am »
With the current launch cadence and a decent stock of first stage cores, there's no real worry about the 7 days or so it takes to get a core that lands on the ASDS back to the Cape as they'll only be flying once every 2-3 months.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3213
  • Fife
  • Liked: 1664
  • Likes Given: 1973
Re: First stage rocket hop back to the launch site
« Reply #10 on: 09/16/2018 09:47 am »
Although it doesn’t seem worth it for F9, SpaceX seems to be rolling this into BFR/BFS. BFS seems fully capable of landing somewhere to deliver passengers or cargo that has only limited propellant loading capacity then taking off again for a short hop of a few hundred or thousand miles to get back to a major spaceport that can launch it on top of a BFR booster. Hop back to a launch site.

Be careful about those numbers, the required propellant goes up fast.

BFS gets to orbit with around 150 tons payload, and if you assume that capacity includes the propellant used to land, that means you get down with 150 tons of payload.
If you swap out half of that payload for propellant, you land with 75 tons.
Landing again at the far end costs 15 tons, leaving you 60 tons.
That gives you 1500m/s, or a range in the order of 200km, not counting drag and the range using all of the payload as fuel is only around 500km.
This is without including drag, and ignoring real life.

You have problems operationally getting much beyond a hundred miles, and thousands requires basically the nominal amount of takeoff propellant.
« Last Edit: 09/16/2018 09:48 am by speedevil »

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 28765
  • Minnesota
  • Liked: 8872
  • Likes Given: 5745
Re: First stage rocket hop back to the launch site
« Reply #11 on: 09/16/2018 12:49 pm »
You could refuel in orbit before landing. Weird, but might work.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 11365
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 8413
  • Likes Given: 6752
Re: First stage rocket hop back to the launch site
« Reply #12 on: 09/16/2018 02:05 pm »
(mod) This topic comes up periodically. I don't remember the last thread offhand but it could be crosslinked or merged.

(fan) I don't think this is a good idea. That said, I don't think the ASDS would need subcooling facilities, if you're just returning, you don't need to fill the tanks all the way much less subcool. As for the nose code problem, is there any chance that a trajectory with less dynamic pressure could be used? Again, you're not trying to loft a payload, just fly back. You wold have propellant to spare
"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 wes_wilson

  • Armchair Rocketeer
  • Full Member
  • *
  • Posts: 132
  • Florida
  • Liked: 62
  • Likes Given: 102
Re: First stage rocket hop back to the launch site
« Reply #13 on: 10/06/2018 04:38 pm »
Each time this comes up, I wonder what the point to point transportation capabilities of BFS (alone, without BFR) would be like on Mars.  How much cargo and people could a refueled BFS move around mars?  Could it take cargo someone and return on one tank of gas?  Would ability to refuel and hop allow for multiple colonies serviced from one central refueling and repair depot on the ground?  Could the fueling facilities be somewhere near water, like the poles, while the colony is somewhere scenic, like with a nice view of Olympus Mons?  Just curious if the p2p capabilities for BFS are also the starting of the martian global transport system. 



 

@SpaceX "When can I buy my ticket to Mars?"

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3213
  • Fife
  • Liked: 1664
  • Likes Given: 1973
Re: First stage rocket hop back to the launch site
« Reply #14 on: 10/06/2018 04:45 pm »
Each time this comes up, I wonder what the point to point transportation capabilities of BFS (alone, without BFR) would be like on Mars.  How much cargo and people could a refueled BFS move around mars?
A fully refuelled BFS can get from surface to LMO and land over 300 tons of payload anywhere on Mars. (modulo landing pad questions)
It can perhaps if delivering a very small payload (tens of tons instead of 300) take off again, and return anywhere on Mars.

It's about 4.5km/s for takeoff - LMO, and landing.

Online CuddlyRocket

Re: First stage rocket hop back to the launch site
« Reply #15 on: 10/06/2018 10:21 pm »
How much cargo and people could a refueled BFS move around mars?

A fully refuelled BFS can get from surface to LMO and land over 300 tons of payload anywhere on Mars.

Subject to structural integrity, of course! :)
« Last Edit: 10/06/2018 10:21 pm by CuddlyRocket »

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3213
  • Fife
  • Liked: 1664
  • Likes Given: 1973
Re: First stage rocket hop back to the launch site
« Reply #16 on: 10/06/2018 10:32 pm »
How much cargo and people could a refueled BFS move around mars?

A fully refuelled BFS can get from surface to LMO and land over 300 tons of payload anywhere on Mars.

Subject to structural integrity, of course! :)
Martian gravity is ~1/3 earths.
The force of a landed BFS at 400 tons is equivalent to 150 tons on earth, about nominal earth payload - before wind loads.

To a prepared pad, at least.
For initial takeoff, the mass is modestly higher compared to mars nominal, but only by some 20% or so. (And remains >200 tons payload even if you cap the mass at the nominal takeoff mass.)

Online CuddlyRocket

Re: First stage rocket hop back to the launch site
« Reply #17 on: 10/09/2018 09:31 pm »
How much cargo and people could a refueled BFS move around mars?

A fully refuelled BFS can get from surface to LMO and land over 300 tons of payload anywhere on Mars.

Subject to structural integrity, of course! :)
Martian gravity is ~1/3 earths.
The force of a landed BFS at 400 tons is equivalent to 150 tons on earth, about nominal earth payload - before wind loads.

To a prepared pad, at least.
For initial takeoff, the mass is modestly higher compared to mars nominal, but only by some 20% or so. (And remains >200 tons payload even if you cap the mass at the nominal takeoff mass.)

The weight on Mars of a given mass of payload will be 38% that on Earth, but the loads due to acceleration and deceleration will be exactly the same as they depend on mass not weight.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3213
  • Fife
  • Liked: 1664
  • Likes Given: 1973
Re: First stage rocket hop back to the launch site
« Reply #18 on: 10/09/2018 09:40 pm »
The weight on Mars of a given mass of payload will be 38% that on Earth, but the loads due to acceleration and deceleration will be exactly the same as they depend on mass not weight.
This is of course correct, but only somewhat relevant.
Having the engines at 40, not 10% maximum thrust on landing doesn't affect the accuracy of your landing solution.
This means you can easily tell if you're in fact able (through exhibited performance) to hit the pad with a velocity low enough that you have margin to safely do the above. The lower gravity and lack of meaningful wind help with solution accuracy, compared with earth, and the higher mass may reduce issues around engine transients.

For takeoff, it's less relevant, as if you've managed to screw up getting off the ground, things have gone very badly wrong.
For merely one-directional P2P orbital hops, without large extra cargo or return capability, there is no extra risk, as you are landing at the nominal mass for landing on Mars.

Tags: