Discussion Elon Musk: the F9 first stage can reach orbit as an SSTO.

[Urwumpe]

Slightly off topic..
Pizza and beer, says that if the falcon gets to final test flight.. it'll fall apart on the way up, due to weak structure.

It looks like it needs a redesign if it's going to work as proposed.
:facepalm:

I would not be too hard on SpaceX.


At least they can claim that their Falcon 9 1.1 rocket has less NOX emissions than a Volkswagen.

 

[Notebook]

I think anything has less NOX emissions than a Volkswagen...:dry:

N.

 

[Urwumpe]

I think anything has less NOX emissions than a Volkswagen...:dry:

N.

Except ships. Those are "waste fuel in, waste emissions out". :lol:

 

[RGClark]

You can't build a rocket stage from love and air alone. The 9 engines alone already weight 4200 kg. 5% of the 380 tons is 19 tons - so you have less than 15 tons left for tanks, propellant utilization and structure. The engines need 18 propellant lines with 10 cm diameter. Strong enough to survive not just the tank head pressure, but also the inevitable water hammer, when you close the valves for shut down or if you just throttle the engines.
A tiny soda can is just 0.07 mm thick at the top and 0.15 mm thick at the bottom - but keeps about the same pressure inside as a much larger Falcon 9 tank. The wall thickness of a tank capable of holding the same pressure and being made of the same material scales up linear by inside diameter: So without any special optimizations about the welds used for the tank or internal stiffeners, the tank would already need 3 mm thickness on the average - with some optimizations you can get this down to tapering between 1.5 and 2.5 mm.
The rocket itself is quite long. If you would use 2 mm thin aluminum for the tanks, a 40 meter long tube with 3.66 m diameter would already weight 5 tons. Now add anti-sloshing devices, propellant utilization, valves, the bulkheads for the tanks, stiffeners for getting the loads of the engines transfered to the second stage (or payload)... and you will be around 8 tons, and have only 7 ton left for all the rest. Thrust structure is harder to estimate, because it depends on many factors. But you can be sure that it is likely almost as heavy as the tanks themselves, because it has to transform the forces of the engines into forces that don't break rocket, especially the vibrations of the engines and the vibrations by the hydraulic TVC system have some effect there. Also the more engines you have, the heavier this structure will be. So, lets be nice and say it weights just 4 tons. 3 tons left.
Now you need to get the propellant into the engines. So, you will have 18 short pipes with 10 cm diameter, one short 30 cm pipe for the Kerosene tank and a long 30 cm pipe inside the Kerosene tank for the LOX (30 cm means the same cross section as nine 10 cm diameter pipes), include some bellows to allow the pipes to survive the vibrations... About 2 tons of mass, likely more (The pipes have to withstand some stronger changes of static pressure than the tanks). Now you have only one ton of mass free for all the electric power subsystem equipment (batteries, power controls), all the GNC electronics that you need, all the pressurant bottles and all the radio antennas, receivers, data handling, you name it. All fits barely into the 5% budget and I had been pretty optimistic in the numbers.
Now, where do you think you can reduce the mass to get below 5%? I have already calculated pretty optimistic, the second stage of the Saturn V did also just barely reach the 5% limit back then (No important electronics and much lower thrust to weight)
The second stage of the Falcon 9 could get below the 5% easily and even with very conservative calculations. But for getting even slightly below 5% for the first stage, you would need to assume perfect magic welds (Structure acts like it was made in one piece) and no safety margins too often. 5.5% (2.5 tons more dry mass) would still be a great lightweight structure, but far more realistic in its assumptions.
And in case you think about it: You can't make a thrust structure for a rocket purely of composites. The vibrations make it very hard to use composites there, only the few static parts of it allow it. Otherwise, you risk that fatigue shredders your rocket during launch - nobody has yet managed to find a way to make composites vibration-resistant and light at the same time, despite the huge demand for such a magic material.
Composites work great for interstages - but the Falcon 9 SSTO does not have many of those.

NASA has a a launch performance calculator that also gives a 16.6 metric ton payload to LEO for the expendable version of the F9 v1.1:

NASA Launch Services Program's
Launch Vehicle Performance Web Site.
http://elvperf.ksc.nasa.gov/Pages/Query.aspx

On this query page enter 200 km for the altitude and 28.5 degrees for the launch inclination to match the latitude of Cape Canaveral, otherwise the payload will be reduced.

Try your calculations again using 16.6 metric tons as the payload to LEO of the expendable F9 to see what the first stage mass fraction would be.

Bob Clark

 

[Urwumpe]

This one is the most recent user guide for the Falcon 9, maybe this is more helpful for you.

http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf

This is the legal binding data for customers and it gives a maximum payload mass of 10,800 kg or 24,000 lbs.

 

[Col_Klonk]

http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf

This is the legal binding data for customers and it gives a maximum payload mass of 10,800 kg or 24,000 lbs.

Has SpaceX signed on any customers yet ?
They'll might be in for a rough ride if they've gone the 'crowd funding route'.
Actually it might be easier just to let the payload 'disappear into space' and then claim insurance.
It'll be interesting to get hold of Insurance company's POV on this future operation. :thumbup:

 

[MaverickSawyer]

Regardless of whether or not it's SSTO... It's NOT a reusable SSTO, so there's no point in SpaceX actually DOING this. It's Elon Musk grabbing at straws to protect an incredibly fragile and large ego from the harsh reality that he's NOT the only player in the reusable spaceflight game.

 

[RGClark]

This one is the most recent user guide for the Falcon 9, maybe this is more helpful for you.

http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf

This is the legal binding data for customers and it gives a maximum payload mass of 10,800 kg or 24,000 lbs.

The passage about the payload is on page 15:

3.3 Mass Properties The payload attach fitting (PAF) converts the diameter of the launch vehicle to the standard 1575-mm (62.01 in.) bolted interface (Figure 3-1). SpaceX uses one of two PAFs on the launch vehicle, based on payload mass. The light PAF can accommodate payloads weighing up to 3,453 kg (7,612 lb), while the heavy PAF can accommodate up to 10,886 kg (24,000 lb). Payloads must comply with the mass properties limitations given in Figure 3-2. Payload mass properties should be assessed for all items forward of the payload attach fitting 1575-mm (62.01 in.) bolted interface (Section 5.1.1), including any mission-unique payload adapters and separation systems. Mass property capabilities may be further constrained by mission-unique payload adapters, Figure dispensers or separation systems. 700 31 : SpaceX payload attach fitting 600 500 CG Height [cm] 400 300 200 100 0 0 2,000 4,000 6,000 Light PAF Heavy PAF EELV, 62 in interface (for reference) 8,000 Payload Mass [kg] 10,000 12,000 Figure 3-2: Maximum allowable center-of-gravity height above the 1575-mm plane SpaceX requires that customers verify the mass properties of their system through measurement before shipping it to the launch site, and the company may request insight into relevant analyses and testing performed. Falcon 9 may be able to accommodate payloads with characteristics outside the limitations indicated in this section. Please contact SpaceX with your mission-unique requirements.

But on the SpaceX web page the payload capacity to LEO is listed as 13,150 kg:
http://www.spacex.com/falcon9

Again though Gwynne Shotwell has indicated this is for the reusable version. The expendable one is 30% higher, which would put it in the 16 metric ton range. She discusses this at the 9 minute mark in this audio interview:

http://www.thespaceshow.com/detail.asp?q=2212

Bob Clark

 

[Urwumpe]

Regardless of whether or not it's SSTO... It's NOT a reusable SSTO, so there's no point in SpaceX actually DOING this. It's Elon Musk grabbing at straws to protect an incredibly fragile and large ego from the harsh reality that he's NOT the only player in the reusable spaceflight game.

Actually, RGClark is the only person who wants a Falcon 9 SSTO at all costs. Purely academic. Elon Musk has only stated that the performance of the first stage is barely enough to reach orbit with a minimal payload.

---------- Post added at 10:34 AM ---------- Previous post was at 10:32 AM ----------

Feel free to order a Falcon 9 v1.1 launch for a 16 ton payload. I wouldn't discuss any SLAs with them then. :rofl:

 

[MaverickSawyer]

Actually, RGClark is the only person who wants an SSTO at all costs.

Fixed that for you.

 

[Hlynkacg]

Has SpaceX signed on any customers yet ?
They'll might be in for a rough ride if they've gone the 'crowd funding route'.
Actually it might be easier just to let the payload 'disappear into space' and then claim insurance.
It'll be interesting to get hold of Insurance company's POV on this future operation. :thumbup:

Is that a serious question or are you suggesting that SpaceX stole ABS-3, SES-8, Thiacom 6, etc... and launched them without the owners' knowledge?

Just looking at the Falcon 9 launch history I count 9 commercial launches thus far, I'm assuming that SpaceX was getting paid for those.

 

[Urwumpe]

Just looking at the Falcon 9 launch history I count 9 commercial launches thus far, I'm assuming that SpaceX was getting paid for those.

Yes, but I doubt that SpaceX was making a profit with those. The customers usually haggle hard for a large bargain on the first launches of a launch vehicle.

 

[Hlynkacg]

It would be rather difficult for a nonexistent customer to haggle.

 

[Col_Klonk]

Is that a serious question or are you suggesting that SpaceX stole ABS-3, SES-8, Thiacom 6, etc... and launched them without the owners' knowledge?

Huh ?

I'm thinking of a hypothetical situation where SpaceX, using investors money, developing the reusable staged rocket, and quoting prices based on that.
So if the reusable thing doesn't work out, any 'shortfall' have to be made up in the contracts.

Now this is when company CEO's/accountants get ingenious or plain stoopid (depending on how you look at it, and/or whether they can get away with it ?).
Every high risk object is insured and I'm sure SpaceX has a lot of insurance.
There is a possibility of temptation (if you can cover up well) to make 'accidents' happen - and leave it up to the insurers to work it out.

This is done all the time by shifty people.... sometimes even encouraged by insurers.

 

[Thunder Chicken]

This is done all the time by shifty people.... sometimes even encouraged by insurers.

Yeah, but basing the success of your business model on insurance fraud is pretty risky, don't you think? How many engineers are able to put eyeballs on that rocket, looking for flaws?

The flaw here is the same flaw that shoots down the moon hoaxers - if there was a hoax of this magnitude, a lot of people would have to know about it and keep quiet. That never happens. because people.

It is much easier to just build the rocket to fly, do triple somersaults, and land softly on a barge, all more than once, than to maintain this fraud.

 

[Col_Klonk]

It only happens once when you desperate...

Besides.. the moon is a hoax.. the camera doesn't lie

 

[Frilock]

SpaceX can't melt steel beams!

 

[RGClark]

The importance of doing the F9 first stage launch as an SSTO, even at low or little payload, is that it would remove the mental block that SSTO's can't be done at all.

Then it would be accepted that, running the numbers, the payload with altitude compensation would be quite significant.

In fact, in that blog post I cited above, the price per kilo then can be even less than for a TSTO. The reason is because altitude compensation increases the payload for a SSTO to such a large extent and also because the cost for the upper stage is a significant portion of the cost for a TSTO.


Bob Clark

 

[Urwumpe]

The importance of doing the F9 first stage launch as an SSTO, even at low or little payload, is that it would remove the mental block that SSTO's can't be done at all.

Hello.... read again: Nobody denies that it is technologically feasible to build a SSTO.

Everybody just knows that it is economically foolish to build one at the current technological variables.

If you can find a billionaire, you can sure build a SSTO without a purpose except getting launched once for millions of USD to show that it is possible.

 

[Hlynkacg]

Minor quibble.

Most people agree that SSTO is possible but is not feasible.