Comments on: Powered landing, analytical solution

By: gravityloss

gravityloss — Thu, 16 Sep 2010 21:56:08 +0000

Marti Sarigul-Klijn also had derived something like this earlier, I ran into it in one of his papers later after I had written this post.

By: gravityloss

gravityloss — Thu, 16 Sep 2010 21:54:29 +0000

NASA report? I think it goes further back than that, maybe Leibnitz or Newton. It’s simple enough that it was derived from first principles.

By: Igor Rozenberg

Igor Rozenberg — Thu, 16 Sep 2010 04:14:55 +0000

G’day gravityloss,

Thank you for an elegant solution – I used it to estimate solid propellants for new Russian manned spacecraft (TPK NP).
Would you be so kind to reference a NASA report you used for analytical solution?
Regards from DownUnder.

By: Matt Jessick

Matt Jessick — Fri, 10 Apr 2009 03:42:57 +0000

(sorry, typing too fast with emacs fingers)
… at Boeing who were considering an optional aero controlled way to flip the vehicle around rapidly and catching it so that the back end could be pointed down for landing. Another group somewhere was concerned with analyzing whether it was reasonable for the engine to remain firing during this sort of gyration. Sadly, I don’t recall the conclusion for that concern…

By: Matt Jessick

Matt Jessick — Fri, 10 Apr 2009 03:35:39 +0000

>>Layne Cook
I stumbled on this blog a little by accident. I hope you don’t mind me adding a few cents worth. I was deeply involved in a sometimes-contentious VL vs. HL debate at McDonnell Douglas during the X-33 proposal back in the mid nineties. It got a little nasty at times, and when we picked a VL for the proposal, Boeing pulled out and went home. We won that battle, but lost the war (to Lockheed).
————–

I worked on the proposal from the Boeing side, working actuator req. I recall sitting beside the controls guys

By: Drag: Loss in Ascent, Gain in Descent, and What It Means for Scalability « Gravity Loss

Thu, 10 Jan 2008 22:57:52 +0000

[...] very first post in the whole blog derived the analytical solution for delta vee in a vertical powered landing that [...]

By: Powered landing, practical considerations (1-dim) « Gravity Loss

Powered landing, practical considerations (1-dim) « Gravity Loss — Sun, 07 Oct 2007 18:14:54 +0000

[...] 7th, 2007 by gravityloss There was some excellent commentary in the last post, and that has partly been one inspiration in writing this [...]

By: gravityloss

gravityloss — Sat, 06 Oct 2007 18:29:48 +0000

Thanks for the good comments.

Doug, yeah, cool, that alternate text thing works, didn’t know that. I don’t know what the S in your equation is, but yeah it makes sense to do it that way, by reducing the throttle smoothly to enable just hover in the end. (In my solution the throttle is increased to maintain deceleration, since the drag helps less and less at lower velocities.)
I’ll write about that more later and an alternative.

And Layne, big thanks, it’s so damn cool to have someone from the DC-X project and X-33 competition commenting on the first real post of my blog!
The lateral channel I had not thought about so much, but it makes a lot of sense of course.
One body length.. That’s quite bold. But maybe your guidance was so good (F-15 laser gyro, right?)
All good info about the startup altitude raising too, great stuff, I will take this in the input for my next post on the subject.

By: Layne Cook

Layne Cook — Fri, 05 Oct 2007 00:11:26 +0000

I stumbled on this blog a little by accident. I hope you don’t mind me adding a few cents worth. I was deeply involved in a sometimes-contentious VL vs. HL debate at McDonnell Douglas during the X-33 proposal back in the mid nineties. It got a little nasty at times, and when we picked a VL for the proposal, Boeing pulled out and went home. We won that battle, but lost the war (to Lockheed).

I like your powered landing impulse and penalty formulae. They offer a quick “absolute minimum” propellant estimate. As you noted, it will be larger after real-world effects are factored in. Another thing you have to budget for is error in the lateral channel. If the lateral guidance and navigation errors can’t be nulled by engine startup time, then that usually means you’re going to have to stay in the air a little longer. For the DC-X, we targeted a point about one body length above the landing target at the end of the high-thrust deceleration, then dropped the last forty or so feet at a constant 3 or 4 feet/sec.

The landing propellant requirement can be an emotional thing too, especially if somebody’s riding in the vehicle! We found our engine startup altitude constantly being raised by the need to allow for contingencies such as engine startup failure (and having to start a backup) or allowing time and space for a crew to punch out if they wanted.

But, in my opinion, VL is still the best way to go for many RLV missions. It always comes down to the complete mission requirements. But its good to see you guys working on it.

By: Doug Jones

Doug Jones — Thu, 04 Oct 2007 17:37:21 +0000

You may be able to eliminate the hover if you add a finagle factor to the acceleration of about 1.3:

a = 1.3*2S/V if I recall correctly.

This excess acceleration ramps down linearly during descent and brings the thrust to hover at touchdown. You can add an offset altitude and velocity target to allow for measurement uncertainties.

As for the Latex text, right-click & look at the properties of the generated images- the alt text has the original code, you can just highlight, copy, & paste.