Author Topic: Mini-BFR ship F9 Second Stage  (Read 36255 times)

Online Tulse

  • Full Member
  • *
  • Posts: 130
  • Liked: 70
  • Likes Given: 0
Re: Mini-BFR ship F9 Second Stage
« Reply #180 on: 11/08/2018 03:33 PM »
But Starlink might be willing to do mods to its payload attachment if it helps advance BFS, and especially if this approach makes the S2 reusable (eventually).  Those things could ultimately lower launch costs for Starlink, and given their launch volume, a little risk up front might be worth it.

Offline TrevorMonty

Re: Mini-BFR ship F9 Second Stage
« Reply #181 on: 11/08/2018 03:44 PM »
Starlink can still use existing US and fairing , but reuseable US with clamshell would be better.

They could actually use mid air recovery, one of their fleet has helipad to support crew dragon. Wasn't practical for fairing recovery because of need for 2 helicopters and support ships.

With enough in orbit life could use it for recovering starlink satellites for investigation. Bring cargo down from ISS even if it is in something like a Cygnus.

Offline adrianwyard

  • Full Member
  • ****
  • Posts: 970
  • Liked: 185
  • Likes Given: 236
Re: Mini-BFR ship F9 Second Stage
« Reply #182 on: 11/08/2018 03:48 PM »
If this thing is close to a scaled down BFR, then using it to test Mars landing is a great idea. And you don't need to go to Mars to do that; instead you try to 'land' it at 125,000 feet where Earth's atmospheric density is similar.

As was done recently for the 2020 rover 'cute: https://www.jpl.nasa.gov/news/news.php?feature=7269

It may be that it could also test the full flip maneuver and soft landing at zero ground speed. (...and then plummet down from 125K ft.)
« Last Edit: 11/08/2018 03:50 PM by adrianwyard »

Offline su27k

  • Full Member
  • ****
  • Posts: 1158
  • Liked: 873
  • Likes Given: 76
Re: Mini-BFR ship F9 Second Stage
« Reply #183 on: 11/08/2018 04:06 PM »
This vid by Scot Manley basically says what I was thinking, but with much higher production values.

Summary
* Merlin powered
* Current faring
* Current deployment mechanisms
* Smallest changes to current stage that still allows for relevant testing, ie not BFS outer mould line.
* Use margin already available on F9 to allow for added recovery hardware, maybe move from RTLS to ASDS if more needed.

The big thing is that there would be no impact on customers, no changes needed to payloads.
How does it properly test the aerodynamics during reentry if the nose of the stage is just the usual payload adapter, and the attachment surface the fairing used? Doesn't that ruin everything?
The aerodynamic nose of the BFR is for accent, in this case the normal fairing does the job. On entry the stage is coming in  sideways and the the TPS will need to account for this. However you can't change the payload attachment mechanism without effecting the customer and you don't want to do that. The payloads need to be interchangeable between the upgraded second stage and the original second stage incase either the payload or stage slips. The customer needs to be  happy to pay for a ride even thought the whole rocket is going through incremental changes, after all they are the ones ultimately paying for the experiments.

Or you can forget about the customer/payload/attachment and just launch it alone as a test vehicle, avoids tons of trouble and speed everything up.

I think people are too attached to the idea of doing test on customer flights. Granted that's what SpaceX ends up doing for F9 first stage recovery, but they didn't start recovery testing this way. Remember they built a brand new first stage called F9R-Dev2 just to do test flight, and then abandoned it when it's no longer useful. SpaceX is not afraid of spending money on test hardware.

Offline nacnud

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2361
  • Liked: 551
  • Likes Given: 229
Re: Mini-BFR ship F9 Second Stage
« Reply #184 on: 11/08/2018 04:09 PM »
Why do people want to turn this into an all singing all dancing magic mini BFR ship?

SpaceX needs data from a hard to access fight regime. Every time they launch a F9 the second stages passes through this flight regime on its way to play with the fishes. Adding a small amount of hardware to the second stage gets spacex the data it needs and the customer pays for the flight.

Anything beyond that is not what has been announced.

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 4302
  • California
  • Liked: 3746
  • Likes Given: 2298
Re: Mini-BFR ship F9 Second Stage
« Reply #185 on: 11/08/2018 04:14 PM »
Starlink can still use existing US and fairing , but reuseable US with clamshell would be better.

Would it - are you sure? An F9 modification with a reusable clamshell would take a hit in payload mass and volume. Both would reduce the number of Starlink sats that can be launched in one launch.

You might argue that this will be offset be upper stage reuse, but there is no firm indication that this variant will be reused or even recovered. So there might not even be any cost savings.

So the big question is what the main purpose of this is:
A) to test BFS technology
or
B) allow faster/cheaper deployment of Starlink.

We know it is A... But it is also B? We don't know. Those goals may actually be in conflict if this US variant has less capability and costs more.

Offline Norm38

  • Full Member
  • ****
  • Posts: 1144
  • Liked: 521
  • Likes Given: 755
Re: Mini-BFR ship F9 Second Stage
« Reply #186 on: 11/08/2018 04:46 PM »
I don't see this test article having any payload, not at first.  If they're building something new, they'd have to convince a customer to accept the risk of something unexpected happening on accent.  Lots can go wrong at MaxQ with new aero surfaces sticking out.

Customers will have already paid for the flight, by paying for the first stage.  They will use a reused booster, maybe one that will set a flight number record (4,5, etc), with a high probability of getting the 1st stage back.

So this test costs SpaceX the custom once-used test article, and fuel.

Offline RedLineTrain

  • Full Member
  • ****
  • Posts: 740
  • Liked: 452
  • Likes Given: 473
Re: Mini-BFR ship F9 Second Stage
« Reply #187 on: 11/08/2018 04:51 PM »
It doesn't seem like mere coincidence that both this upgraded stage and the Starlink satellites are supposed to first fly mid-year 2019.
« Last Edit: 11/08/2018 04:54 PM by RedLineTrain »

Offline Slarty1080

  • Full Member
  • *
  • Posts: 199
  • UK
  • Liked: 55
  • Likes Given: 20
Re: Mini-BFR ship F9 Second Stage
« Reply #188 on: 11/08/2018 05:00 PM »
I would be interested in peoples opinions

Known
F9+modifier stage 2 (Small Falcon Ship SFS?) to do orbital-hypersonic re-entry testing of TPS and control surfaces as this aspect is difficult to simulate.
Planned to launch in just 7 months
Full BFR dev ship will do supersonic through landing tests in Boca Chica, Texas

Implied
Will use existing M-Vac in second stage or possibly Merlin-SL. Assume Raptor will not be used because it would add so much complexity – 3 propellants instead of 2, redesign of pressurization system (He) and ignition system (TEA/THB)

Probable
It may be recovered but will not be reused. probably a water landing with chutes or air capture.
Existing materials will be used no composite tanks. IMO to keep things simple.

Unclear
Will it carry a payload? IMO Yes
Will it use the existing fairing or variant of it? If not then how will this impact existing customer’s adaptors? And could it be used just for starlink? If it will use the existing fairing then how will the second stage / fairing be configured into a suitable re-entry test form after the sat has been launched? (what is deployed or jettisoned after sat deployment but before re-entry
Will it be used for Orbital refuelling tests?
Will it be just a 3.7m scale model of the BFR or will it incorporate a payload fairing in any form? Possibly related question what is the diameter of the starlink sats?
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline Slarty1080

  • Full Member
  • *
  • Posts: 199
  • UK
  • Liked: 55
  • Likes Given: 20
Re: Mini-BFR ship F9 Second Stage
« Reply #189 on: 11/08/2018 05:05 PM »
I don't see this test article having any payload, not at first.  If they're building something new, they'd have to convince a customer to accept the risk of something unexpected happening on accent.  Lots can go wrong at MaxQ with new aero surfaces sticking out.

Customers will have already paid for the flight, by paying for the first stage.  They will use a reused booster, maybe one that will set a flight number record (4,5, etc), with a high probability of getting the 1st stage back.

So this test costs SpaceX the custom once-used test article, and fuel.

I agree first flight will be a true test flight. After that they will try to fly other payloads to piggy back their Small Falcon Ship tests on
The first words spoken on Mars: "Humans have been wondering if there was any life on the planet Mars for many decades … well ... there is now!"

Offline speedevil

  • Senior Member
  • *****
  • Posts: 3046
  • Fife
  • Liked: 1530
  • Likes Given: 1794
Re: Mini-BFR ship F9 Second Stage
« Reply #190 on: 11/08/2018 05:07 PM »
We know it is A... But it is also B? We don't know. Those goals may actually be in conflict if this US variant has less capability and costs more.
We don't even know if there aren't multiple projects going on at once.

A low risk/reward near-stock F9S2, using balloon deceleration and low peak heating entry, aimed at starlink deployment and nothing else, capable only of LEO, and not really capable of scaling to GEO or doing much beyond getting to LEO and back and taking a moderate payload hit.

A 'high risk/reward' 'mini-BFS'.
Something like CF+TPS BFS-chomper aeroshell with a flexible enough envelope that it can manage kerosene or methane, aimed at parachute recovery, with a route to landing.

It starts off much like the low reward version, only it has a more aggressive TPS directly useful for informing on BFS, and parachute recovery.
Recover it a couple of times, and swap out the mvac for a raptor, taking a moderate hit on performance due to minimum throttle on raptor for some payloads.
Recover it a couple more times, add three BFS RCS thrusters and recover much of that performance hit as you can use them as a low thrust terminal engine.
Now try propulsively landing it, or adding this mode as a backup for a 'hail mary' if the weather is inappropriate for parachutes.

If the high risk does not work, you're out the cost of a couple of shells, and have learned what you hoped to learn to inform BFS development.

If it does work, you've got an capable second stage that could do really quite interesting things, especially on FH.

If BFR does not come along as expected, you've got a nice backup low cost launch method in either the basic or advanced stage.

If it does work, you've got a nice high energy third stage that makes payload to GEO easy, or single launch of BFR moon landings with a small payload.

Investing a non-trivial amount of money now to ensure you have access to low-cost launch for the bulk of starlink would make an lot of sense.

Multiple parallel designs - perhaps with various levels of effort may directly lead to immediately useful products, but they are also useful to prove out components and design teams.



Offline Dave G

  • Senior Member
  • *****
  • Posts: 2212
  • Liked: 941
  • Likes Given: 1176
Re: Mini-BFR ship F9 Second Stage
« Reply #191 on: 11/08/2018 05:11 PM »
there is no firm indication that this variant will be reused or even recovered. So there might not even be any cost savings.

Yes.

In fact, there are indications that it won't be recovered, like Musk's follow-up tweet about no propulsive landing, and this:

Quote from: Gwynne Shortwell
The second stage is not designed for reuse on the Falcon 9 or the Falcon Heavy. However, we do want to bring it back slowly. Currently, it reenters but too hot. On missions with extra propellant, we want to bring it back to see how it behaves, not to recover or reuse. This data will be very valuable.
https://www.flickr.com/photos/jurvetson/37659376821

Offline rpapo

  • Cybernetic Mole
  • Full Member
  • ****
  • Posts: 1196
  • Michigan, USA
  • Liked: 630
  • Likes Given: 483
Re: Mini-BFR ship F9 Second Stage
« Reply #192 on: 11/08/2018 05:20 PM »
I seem to remember people talking about a "Franken-stage" being developed for the initial Falcon Heavy launch.  Some SpaceX employee had made that comment back in mid-2017 or so, and the reference was to something being developed for testing second stage reusability.

Might those references have been to the early stages of his Mini-BFR project?

(Unfortunately, I can't seem to find the NSF forum posting that mentioned it...)
An Apollo fanboy . . . fifty years ago.

Offline groundbound

  • Full Member
  • **
  • Posts: 213
  • Liked: 174
  • Likes Given: 8
Re: Mini-BFR ship F9 Second Stage
« Reply #193 on: 11/08/2018 05:57 PM »
I have a question for the assorted rabble in this thread: something about which I'm wholly ignorant.

ISTM likely that SpaceX has the following goals, probably along with many others.

1) They want information from this the most, especially about the hypersonic deceleration regime.

2) They are somewhat willing for things to go wrong, for several definitions of "wrong," as long as they succeed in 1) above.

So the question is this. How plausible is it that they can do high data rate live telemetry through hypersonic flight? Alternatively, how easy is it to throw together a flight data recorder and ocean locators system?

Offline lrk

  • Full Member
  • *
  • Posts: 135
  • Minnesota
  • Liked: 44
  • Likes Given: 402
Re: Mini-BFR ship F9 Second Stage
« Reply #194 on: 11/08/2018 06:43 PM »
I seem to remember people talking about a "Franken-stage" being developed for the initial Falcon Heavy launch.  Some SpaceX employee had made that comment back in mid-2017 or so, and the reference was to something being developed for testing second stage reusability.

Might those references have been to the early stages of his Mini-BFR project?

(Unfortunately, I can't seem to find the NSF forum posting that mentioned it...)

That was an L2 post, FYI.  But it was later clarified that all this meant was that the stage was a hybrid of block numbers. 

Online docmordrid

  • Senior Member
  • *****
  • Posts: 5020
  • Michigan
  • Liked: 2132
  • Likes Given: 1
Re: Mini-BFR ship F9 Second Stage
« Reply #195 on: 11/08/2018 06:50 PM »
My now evolved guess is a dedicated test vehicle with a close to full fidelity outer mold line. F9 S2 subs for the BFS propulsion module/tanks. May not use the MVac nozzle extension. The rest is a CF layup & ballast.
 
Validates the aerodynamics up and down, and tests the fins during a Skydiver descent.

A landing must be done to evaluate the thermal protection system(s) so it needs a basic guidance system,  a return mechanism, and an RCS.

ISTM all these can be done using items already tested for fairing recovery; cold gas thruster RCS, a riff of the fairing guidance system, and the GPS guided parafoil (but larger.)

Dedicated test flights using a high mileage Flight Proven™ booster.
DM

Offline Rocket Science

  • Senior Member
  • *****
  • Posts: 8925
  • NASA Educator Astronaut Candidate Applicant 2002
  • Liked: 2822
  • Likes Given: 7430
Re: Mini-BFR ship F9 Second Stage
« Reply #196 on: 11/08/2018 06:52 PM »
They could also try a steerable parafoil and land recovery on skids such as on the X-38...
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline mme

  • Full Member
  • ****
  • Posts: 1280
  • Santa Barbara, CA, USA, Earth, Solar System, Milky Way Galaxy, Virgo Supercluster
  • Liked: 1610
  • Likes Given: 4300
Re: Mini-BFR ship F9 Second Stage
« Reply #197 on: 11/08/2018 08:23 PM »
To summarise (correct me if I've missed something)

'Knowns' (as of today's Elon thinking):
- Mini-BFS layout (blunt cylinder, forward canards, rearward triple fin)
- No propulsive landing due to vacuum nozzle
- Tests lightweight TPS
- Tests hypersonic control surfaces

Good assumptions:
- CF composite construction rather than Al-Li sheet+stringer. Stack a few interstages and cap with an FH nosecone and you have a good outer mould line already using existing tooling.
- Metallic TPS. Already in experimental use as the Block 5 dancefloor insulation, better meets reusability criteria than PICA-X, SpaceX have not demonstrated any other high-performance TPS.
- Non-destructive recovery. With SpaceX, "don;t throw it away if you can help it" is always a good assumption, and recovery allows for rigorous analysis

Probably but arguable:
- Kerolox + M1DVac. While an argument can be made that testing using Methane on the other side of the CF would better replicate BFS conditions (151K colder) that's probably not worth the extra hassle of adding more propellant handling to a pad. Could also be seen as an opportunity to flight-test Raptor long before the BFS hops can begin though, and skips any work on CF Kerosene tankage.
- F9H use only. Allows for higher dry mass through more throw weight.
- Re-use after recovery. Recovering in an intact enough state to examine is reasonable (parachute + moderately splashdown would work for examining the TPS even if it compromises the structure), recovering without groundable damage means mid-air capture or an even-bigger-again net. SpaceX have shield away from the former and still working on the latter with much lighter objects.
- Operation use for payloads, rather than just a pure test vehicle. This is something I could see as an aspirational goal that can be discarded during development if it proves non-viable, but a re-usable upper stage even if with low payload capacity would be useful for Starlink deployment.

I don't think that CF is a "mod to the build tree" nor an "upgrade." My bet is it'll be a modified S2 which means Aluminum. I don't think it's a pure test vehicle, I think it will use a normal fairing and it'll be flown on every mission that is possible based on payload mass and customer willingness. Incremental development, starting with the bare minimum, just like they did with the first stage.
Space is not Highlander.  There can, and will, be more than one.

Offline Dave G

  • Senior Member
  • *****
  • Posts: 2212
  • Liked: 941
  • Likes Given: 1176
Re: Mini-BFR ship F9 Second Stage
« Reply #198 on: 11/08/2018 08:56 PM »

Good assumptions:
- Non-destructive recovery...

I don't believe this is a good assumption. 

I think this is a test vehicle. It's main purpose is to gather data for the real BFS.

Offline NewSpaceIsFun

  • Member
  • Posts: 16
  • Liked: 20
  • Likes Given: 110
Re: Mini-BFR ship F9 Second Stage
« Reply #199 on: 11/08/2018 10:10 PM »
Moved from wrong thread:
====================

I'm kind of wondering about the possibility that this "test bed" F9S2/mini-BFS could be partly a result of the need for a more controllable/capture-able  reusable second stage... Just in case the fairing-capture-gambit is not panning out and you don't want to throw away all those fairings as you are trying to accelerate Starlink rollout. So....reusable smallish-sat deployer! :) Yeah bad mass fraction or whatever, but you get the hardware back each time. Gotta add deploy door/mechanism, extra cold gas, chutes and carrying that integrated "fairing" all the way to LEO reduces usable payload..but we want cheap not high performance. If I'm moving quick/agile and want a quick turnaround this sounds doable as right now I'm the only customer.

If mini-BFS works out ok and is helping reduce Starlink rollout time/costs, and if you give customers with smaller sats a cut in price you might be able reduce S2/fairing manufacturing overhead even more all while having Customers(Starlink is a Customer, right?) pay for dev work. Also note that a fairing half somewhat approximates the aero profile of a falling BFS right? They have a lot of recent experience with that regime, but slower. Of course mini-BFS is probably much heavier than a fairing half when being captured.

Has there been a slowdown in fairing-capture exercises?
How many Starlink sats (gen-1) can a mini-BFS delivery to orbit?
If the net could capture a Dragon, how much more does an almost empty mini-BFS weight?

Also, I'm guessing std lithium-based F9 and Mvac... Moving quick right!!??

Tags: