[AR] Re: Reusable Dragon & Grasshopper delta V (off topic)
- From: Ian Woollard <ian.woollard@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 9 Aug 2014 18:53:32 +0100
That would be the non RTLS version, the RTLS may well separate at slightly
lower speed and then burn the second stage a bit longer to make up for it.
The simulations I've done on this in the past suggest that the overall
delta-v RTLS penalty is actually pretty damn big.
I don't have the exact number to hand but IRC it was something stupid like
2.5km/s.
The only reason the payload penalty they're quoting is as small as it is is
because the vehicle is firmly SSTO class (non reusable) or better; they
have a mass ratio of 96+%, SSTO class is about 95% or slightly less.
Before separation I found that the optimum trajectory tends to drift west,
before burning upwards and east. After separation of the first stage, with
RTLS it needs to do a pretty enormous burn to make it back; but after
losing the second stage, it's much, much lighter so that extra delta-v uses
propellant that is about 1/3 of the second stage mass that it's just shed;
which is mostly where the loss of payload comes from.
The thing I didn't like about al this was that in order for it to work is
that you pretty much have an SSTO class vehicle anyway, and there's less to
choose between going SSTO reusable and just doing the RTLS than you might
expect. I suppose the main thing that SpaceX see is that it's probably
easier to go from a two stage non reusable to two stage fully reusable than
it is to go from two stage non reusable to fully reusable SSTO; and the
market is definitely mostly two stage non reusable right now.
On 9 August 2014 17:29, Hop David <hopd@xxxxxxxxxxx> wrote:
> On 7/31/14 1:57 PM, Bill Claybaugh wrote:
>
>> Mach 10 staging
>>
> That's helpful, thanks. That search string led me to a NSF thread.
>
> http://forum.nasaspaceflight.com/index.php?topic=34464.0
>
>
--
-Ian Woollard
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