Author Topic: SpaceX: General Falcon and Dragon discussion (Thread 2) (Read 625125 times)

rcoppola · « **Reply #1020 on:** 01/17/2011 08:04 pm »

What's the hold up of initiating COTS-D?

meekGee · « **Reply #1021 on:** 01/17/2011 08:08 pm »

2 motors per cluster: on LAS, you fire both. On landing, just one, so have redundancy per cluster. (The LAS doesn't have to be as reliable as a landing system)

I'd go with 5 or 6 clusters though, since you can then have an entire cluster fail and still maintain control. (6 is braindead - you just kill the opposite cluster. 5 is just a bit more complex but can still work)

meekGee · « **Reply #1022 on:** 01/17/2011 08:19 pm »

Quote from: kraisee on 01/17/2011 07:58 pm

Abort systems are some of the hardest design challenges, because they have to start-out assuming most of the worst possible case scenario's have already occurred.

That's a blanket statement that needs a second look from a top system perspective.

If in the course of chasing a very unlikely failure mode you end up adding too much system mass/complexity, then it might not be worth it.

The example given in a previous post - all engines stuck at >100% - is a good one. If the cost of designing to that eventuality is to increase the size of the LAS engines, and the amount of propellant they carry, and thus the size of the parachute, and thus the weight of the capsule, and thus the weight of the rocket.... then someone a top level designer will weigh it all and might decide that overall safety is not enhanced.

Taking it another step, even for the case of all engines stuck at 100%, it is probably cheaper to install an additional (destructive) kill mechanism for the engines then it is to design a stronger LAS engines.

Ben the Space Brit · « **Reply #1023 on:** 01/17/2011 08:24 pm »

Quote from: rcoppola on 01/17/2011 08:04 pm

What's the hold up of initiating COTS-D?

Unlike COTS-C (cargo), the program was never funded. It has been partially superceded by CCDev but, at present, there isn't a single, unified commercial crew transport services program to replace it.

Jkew · « **Reply #1024 on:** 01/17/2011 09:00 pm »

So is there any indication that this is using hypergolics?

I have no expertise in this, but I tried to find a hypergolic engine with the required lbf ( I figured ~145k total across all engines for abort ) and came up empty.

Has anyone built a hypergolic engine before like this?

docmordrid · « **Reply #1025 on:** 01/17/2011 09:11 pm »

The presumption has been they'll use the hypergolic fuel stores already on Dragon for the Draco thrusters - 1290kg of it according to their site.

yg1968 · « **Reply #1026 on:** 01/17/2011 09:12 pm »

Quote from: corrodedNut on 01/17/2011 05:18 pm

And now there's a new update, relating to their CCDev2 proposal:

http://www.spacex.com/updates.php

Some interesting details about their CCDev2 proposal is given in their update:

Quote

On December 13th, we submitted our proposal to NASA’s Commercial Crew Development Program (CCDev2) to begin work on preparing Dragon to carry astronauts. The primary focus of our CCDev2 proposal is the launch abort system. Using our experience with NASA’s COTS office as a guide, we have proposed implementing the crew-related elements of Dragon’s design with specific hardware milestones, which will provide NASA with regular, demonstrated progress including:
-initial design of abort engine and crew accommodations;
-static fire testing of the launch abort system engines; and
-prototype evaluations by NASA crew for seats, control panels and cabin

jabe · « **Reply #1027 on:** 01/17/2011 09:33 pm »

Quote

-........ crew accommodations;

-prototype evaluations by NASA crew for seats, control panels and cabin

curious
is the work on Orion proprietary or can they use what has been learned for the dragon.. A lot of ergonomic work seems to have been done so why waste it if they can use it...

jb

iamlucky13 · « **Reply #1028 on:** 01/17/2011 09:35 pm »

Quote from: docmordrid on 01/17/2011 09:11 pm

The presumption has been they'll use the hypergolic fuel stores already on Dragon for the Draco thrusters - 1290kg of it according to their site.

And someone had done some napkin math assessing whether that would provide sufficient impulse to serve as LAS. If I remember right (not sure which thread to back-track it to), the guesstimate was, yes, it would be sufficient, even assuming poor specific impulse due to the necessarily compact nozzles on the LAS engines.

I'm not sure what they're envisioning as far as combining this with a powered hard-ground landing. Performing an abort on a trajectory that leaves you coming down over land means either you also need enough fuel to brake for touchdown, or your parachute needs to have you moving slow enough for a survivable touchdown.

As far as big hypergolics, the Titan IV first stage engines each produced about 550,000 lb thrust, but it was a big turbopump fed engine, where as the Dragon LAS will need to be pressure-fed and very compact.

Some hints on pricing from the update:

Quote

NASA will be totally dependent on the Russian Soyuz to carry astronauts to and from the International Space Station for a price of over $50 million per seat.

The December 8 COTS Demo 1 flight demonstrated SpaceX is prepared to meet this need--and at less than half the cost.

I'm going to go ahead and assume that's based on 7 occupants, so the per-flight cost is $175 million or less.

Their CRS contract is $133 million per flight, so their target appears consistent with that, allowing a very modest amount extra for the added complexity of the crewed Dragon.

Of course, we're a long ways away from this, so I don't want to encourage anyone reading too much into this; It's what SpaceX seems to think they can do.

docmordrid · « **Reply #1029 on:** 01/17/2011 09:43 pm »

Looking closer at the video the landing gear looks to deploy by simply extending from the heat shield, which would seem to qualify under KISS. There were circular features shown in earlier imagery that look to be in that area.

Ben the Space Brit · « **Reply #1030 on:** 01/17/2011 09:50 pm »

I can honestly say that SpaceX has astonished me with how advanced Crewed Dragon really seems to be. I was honestly expecting parachutes plus power for the last second or so for braking; This is something else!

Lars_J · « **Reply #1031 on:** 01/17/2011 09:58 pm »

Quote from: docmordrid on 01/17/2011 09:43 pm

Looking closer at the video the landing gear looks to deploy by simply extending from from the heat shield, which would seem to qualify under KISS. There were circular features shown in earlier imagery that look to be in that area.

Probably not... Those are the structural pressure pads that are the attachment points for the trunk section.

I'm guessing the gear 'pads' would be round 'tiles' in the heat shield that are extended down.

docmordrid · « **Reply #1032 on:** 01/17/2011 10:04 pm »

Is there any reason why those attachments couldn't be dual purpose - extending when needed? I can't imagine them using a segment of PICA-X as a landing foot.

Space Junkie · « **Reply #1033 on:** 01/17/2011 10:06 pm »

Quote from: Ben the Space Brit on 01/17/2011 09:50 pm

I can honestly say that SpaceX has astonished me with how advanced Crewed Dragon really seems to be. I was honestly expecting parachutes plus power for the last second or so for braking; This is something else!

Remember, that video shows what they hope to do in the long term. The initial crewed dragon will still land in the water.

meekGee · « **Reply #1034 on:** 01/17/2011 10:15 pm »

Actually, I think docmordrid has it exactly right, and if those are the structural transfer points to the rocket, then so much the better - of course you'd want them to be the landing gear, since the dynamic impulse load during touch down can be significant, so you want to transfer it neatly onto the rest of the frame.

Re-using the same structural component - a signature SpaceX move.

As for having heat shield material at the bottom of the landing gear - small price to pay IMO. Even if you have to replace the feet after each landing - small change really.

Cinder · « **Reply #1035 on:** 01/17/2011 10:34 pm »

Quote from: Ben the Space Brit on 01/17/2011 09:50 pm

SpaceX has astonished me with how advanced Crewed Dragon really seems to be.

What SpaceJunkie said - in the video the narration is "next generation Dragon".

docmordrid · « **Reply #1036 on:** 01/17/2011 11:07 pm »

First gen: cargo
Second gen: crew

but with a tons of commonality and cross development going on. No need to reinvent the wheel if you don't have to.

Lars_J · « **Reply #1037 on:** 01/17/2011 11:33 pm »

But there will also be quite the progression between the two. Should a crew Dragon be funded, most of the features would no doubt be tested on cargo Dragons.

But as others have said - Very doubtful that the first generation manned Dragon would do a powered precision landing. Sea landings may occur at first, then land parachute landings (when sufficient precision has been demonstrated), and *then* a powered landing.

docmordrid · « **Reply #1038 on:** 01/17/2011 11:44 pm »

My bet: instead of incrementalism they combine tests where possible; i.e. do a ground landing test when they test the LAS. 2 birds.

Jim · « **Reply #1039 on:** 01/18/2011 12:02 am »

Quote from: meekGee on 01/17/2011 10:15 pm

Actually, I think docmordrid has it exactly right, and if those are the structural transfer points to the rocket, then so much the better - of course you'd want them to be the landing gear, since the dynamic impulse load during touch down can be significant, so you want to transfer it neatly onto the rest of the frame.

Re-using the same structural component - a signature SpaceX move.

As for having heat shield material at the bottom of the landing gear - small price to pay IMO. Even if you have to replace the feet after each landing - small change really.

Not viable. The two tasks require completely different structural dynamics