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#51 2020-12-31 18:17:16

kbd512
Administrator
Registered: 2015-01-02
Posts: 4,237

Re: Landing legs for the BFR

SpaceNut,

In that case, the goal seems even more improbable.  30+ engines and separate sets of propellant feed lines, substantially more propellant, more computers that control the engines, hydraulically actuated grid fins...  I'll put it to you this way- there are a substantial number of checks performed before every flight and it takes time to perform them.  There's no doubt that computers and automation could assist, but only to a point.  The engines will have to be so advanced in anomalous operation or wear detection that no instrumented test fires are required prior to the next flight.  Maybe it's possible, but it almost certainly won't be very practical to operate from more than a handful of specially-equipped sites.  We'll see.  They've accomplished quite a bit already, but this is where we run smack into logistical issues that don't have very good answers, at least at the present time.

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#52 2020-12-31 18:24:33

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 22,148

Re: Landing legs for the BFR

I thought the goal was sort of asking to much in the final seconds while the gantry arm would move to hold it upright before engine cutoff.

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#53 2021-01-01 23:31:50

kbd512
Administrator
Registered: 2015-01-02
Posts: 4,237

Re: Landing legs for the BFR

SpaceNut,

It might actually be more practical for the rocket to be stabilized by a gantry than it would be to assure a completely perfect touchdown, every single time.  The forces involved are huge and vertical landings are always fighting physics, with respect to keeping the vehicle upright.  If both Starship and its Super Heavy Booster were 15m in diameter, therefore much wider and shorter while still containing the same quantity of propellant, or more, then I could see unassisted vertical landings working more in favor of both stages.  A 15m booster would also permit Starship to carry a 7th engine, or an "octaweb" arrangement, providing badly needed thrust.  As GW already pointed out, a fully fueled Starship wouldn't have sufficient thrust to leave the ground under its own power.  15m would also provide a gigantic cargo bay for space telescopes and solar power satellites.  I think a wider vehicle carrying more propellant is what it would take to maintain that 150t to 200t payload performance.  It would also be an opportunity to get rid of that goofy tank design prior to shoving a thrust structure up through the rear tank dome and ruining everyone's day.

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#54 2021-01-02 10:30:59

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 22,148

Re: Landing legs for the BFR

Well I doubt space x will be changing the booster any time soon but more fuel needed for landing would mean an even taller rocket that would see more wind effects at landing while trying to stay stationary while the arms latch to the body.

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#55 2021-01-02 12:12:57

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 6,070

Re: Landing legs for the BFR

For SpaceNut re #54

If you eliminate landing gear altogether, then your mass goes down and your existing fuel load should be more than sufficient to maneuver into capture position at Mars, where the gravity is less and the effect of wind is negligible compared to the mass of a Starship.

I assume you meant "Starship" when you referred to booster above, if you were thinking about landing on Mars.

If you did indeed mean Starship, then your point about not changing the design makes sense, except that the Starship to land on Mars is still on the drawing boards, and the Starship to land on Earth does not yet exist.

There is plenty of time to change the design of the Starship to land on Mars.

The only players I can see on the horizon who might be able to build a landing pad for Elon at Mars are the Chinese or the Russians.  On the other hand, the Indians are showing capability that might stretch that far, and the Europeans could definitely do it but I just don't see a collective will.

Of the players, only the Chinese are (in my opinion) strong contenders, because they have the distinct advantage of an authoritarian form of government, and a (relatively young) dictator-for-life/king in charge.

It might amuse him to offer Elon a sturdy landing pad, and a customs service staffed by loyal Party members.

(th)

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#56 2021-01-02 13:53:47

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 22,148

Re: Landing legs for the BFR

Not starship but first stage is the booster that is reusable in the bar for quick relaunch scheme.

Starship as a coast to coast needs even more tome if it's got engine fuel problems.

Starship was a second stage to orbit would be even harder to land as boiloff would happen and further increase fuel loading.

Also there is the rocket to latch rotation issue for alignment on all flavors using the gantry arms....

Landing gear was a tiny mass that was added to make the falcon 9 and its heavy totally reusable.

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#57 2021-06-06 10:40:00

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 6,070

Re: Landing legs for the BFR

YouTube video showing closeup of landing legs Falcon 9 First stage.

https://www.youtube.com/watch?v=Tox9uu4QtMg

Here's a model of the legs showing possible action: https://www.instructables.com/Building- … ding-Legs/


(th)

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#58 2021-06-09 07:54:03

NewMarsMember
Member
Registered: 2019-02-17
Posts: 101

Re: Landing legs for the BFR

This is a post requested by GW Johnson while we wait for him to be able to post ...

What I wanted to post and could not,  was that I just put a concept design analysis article about Starship landing legs up on my "exrocketman" site.  It deals with the simplest,  most straightforward update of the Falcon-9 landing leg idea reworked for Starship. It complements what I said about landing legs in the just-previous Evaluations of Starship/Superheavy article.

http://exrocketman.blogspot.com/

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Last edited by NewMarsMember (2021-06-09 12:09:00)


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#59 2021-06-09 12:20:14

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 6,070

Re: Landing legs for the BFR

For all regarding GW Johnson's latest blog article:

Final Comments

I started this write-up in March,  intending to complete it and post it during April.  However,  my laptop died,  and took with it a lot of data,  including this write-up.  I was able to recover the data,  so that finishing this write-up became possible.

This article is intended as guide to previous reverse-engineering analyses,  which have evolved over time.  I have identified for the reader which articles have the latest and greatest data,  to which mission scenario they apply,  and exactly how to quickly and easily reach them.   

I am hoping that some of Spacex's engineers are aware of me and what I have done.  I might be able to shorten their learning process a little;  the "school of hard knocks" can be very expensive indeed. 

Posted by Gary Johnson at 2:45 PM

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