SpaceX News

[ladajo]

INteresting glimpse into how ULA sees things. I am not sure I agree with his assessment of the SpaceX model. I think with-in the year we could see SpaceX do a recycle launch.

ULA Commentary on Space Race

[DeltaV]

Beancounters rule. Engineers are serfs. Crunch your numbers and be quiet.

ULA exec resigns after saying firm shied away from price war with SpaceX
http://www.reuters.com/article/us-space ... SKCN0WJ05H

[ladajo]

Now that is freaking hilarious.

That'll learn'im.


Too bad he was hammered for being honest, which is obviously not a treasured asset at ULA.
I hope they go out of business, as that is a prime indicator of government contracting hubris.

[KitemanSA]

So what we are really saying here is that we would strap on pony tanks with a net positive thrust to account for extra fuel mass that will transfer to the central core. Then they would detach and fly back on their own.
What is the real difference between the STS method of solid fuel pony boosters that did the lion's share of pushing, and the SMEs were throttled down to save gas while the boosters were in play? If you wanted more lift/main fuel savings, they could have added more booster power by doubling up on each side. Of course, the external tank would probably have needed some beefing up, but certainly doable with a similar end result.

We must be using the term "net positive thrust" differently. The difference is that the SRBs provided thrust to the core. In general, unless they figure it is beneficial, all the Aux Tanks do is provide fuel (and oxidizer) to the core. It would allow the current high payload F9 to have a flyback core instead of the throw away core with which it is currently configured.

[JoeP]

I'm trying to follow this debate can't seem to follow what Kite is getting at. What am I missing.

Aux tanks add weight but extend burn time. Max thrust is capped to what main engines can deliver. Seems to me like not a great idea, unless the engines are very powerful to begin with and the volume of the main internal tanks has already been locked in via design as undersized to begin with.

Aux boosters add weight, but add thrust, which may be used to save fuel in main tanks (or achieve thrust levels over the ceiling capacity of the the main engines) while they are attached.

I see little reason to tie a booster's fuel source to the main tanks, personally.

[paperburn1]

The first two minutes of flight are intended to move the Falcon to the thinner atmosphere and to the highest possible speed. . To prevent damage from the vehicle due to dynamic pressure that is growing with speed in the dense part of the atmosphere the thrust of the center engines are reduced to around 70% (launch specific) at about 30 seconds into the flight. Throttling up to maximum power occurs after maximum pressure (max Q) stresses are reached. Because air density is dropping fast with growing altitude the pressure ( Max Q) drops in spite of growing speed after that point. Getting above this point as fast as possible and then shedding as much weight as possible greatly increases the load to LEO. So by making sure the main engine cluster has the most fuel at this point(after max Q) then letting the outside engines burn to empty and bringing up the center engine cluster to full power they can effectively lift four times the weight to LEO or GTO. All for the cost for the cost of the fuel and two reusable First stages (If we get that recovery thing down). BAZINGA!

PAYLOAD TO LEO
53,000kg 116,845 lb

PAYLOAD TO GTO
21,200kg 46,738 lb
So bottom line in makes a big difference doing it the way they do. It almost looks like the Spacex people have all three sides of the production triangle working.

[paperburn1]

This statement for ULA shows the short nearsightedness of the company...
“It’s getting tons of press. It’s extraordinarily, engineeringly cool – but it’s dumb,” Tobey said. “I mean: Really? You carried 100,000 pounds of fuel after deployment of the SES satellite [SpaceX’s March launch of the commercial SES-9 telecommunications satellite, to geostationary-transfer orbit] just to try to land on the barge.” -

YEA! for 25000 dollars in fuel you can save 15 million dollars ,after all you have the legs to get it up their so why not?

[Skipjack]

This statement for ULA shows the short nearsightedness of the company...
“It’s getting tons of press. It’s extraordinarily, engineeringly cool – but it’s dumb,” Tobey said. “I mean: Really? You carried 100,000 pounds of fuel after deployment of the SES satellite [SpaceX’s March launch of the commercial SES-9 telecommunications satellite, to geostationary-transfer orbit] just to try to land on the barge.” -

YEA! for 25000 dollars in fuel you can save 15 million dollars ,after all you have the legs to get it up their so why not?

ULA is trying to do damage control. They know that they have nothing to compete with SpaceX. So they resort to badmouthing them. Pitiful.

[krenshala]

I'm trying to follow this debate can't seem to follow what Kite is getting at. What am I missing.

Aux tanks add weight but extend burn time. Max thrust is capped to what main engines can deliver. Seems to me like not a great idea, unless the engines are very powerful to begin with and the volume of the main internal tanks has already been locked in via design as undersized to begin with.

Aux boosters add weight, but add thrust, which may be used to save fuel in main tanks (or achieve thrust levels over the ceiling capacity of the the main engines) while they are attached.

I see little reason to tie a booster's fuel source to the main tanks, personally.

Aux tanks add weight, reduce thrust to weight ratio, but extend the burn time. How much, if any, gain this provides depends on how much "extra" fuel you are adding this way and what this changes for the overall mass (thrust to weight ratio). It is entirely possible for this to make the rocket less efficient or even not make it to orbit.

Between adding more fuel, adding boosters, and adding boosters that can do fuel cross feed, just adding fuel is almost always the worst choice of the three for what delta-v it adds (assuming the same "extra" fuel volume in all three cases). Fuel cross feed gives the biggest boost to delta-v, but at the cost of the additional complexity and equipment weight. Just adding boosters falls somewhere in the middle, depending on the boosters and what fuel they have available.

[paperburn1]

In general I agree, adding TARE weight is generally not a good idea, but these boosters have their own motors as well so you can get a positive tradeoff especially if you loose that weight after the first three minutes of flight. and even more so if recoverable.

[KitemanSA]

I'm trying to follow this debate can't seem to follow what Kite is getting at. What am I missing.

Aux tanks add weight but extend burn time. Max thrust is capped to what main engines can deliver. Seems to me like not a great idea, unless the engines are very powerful to begin with and the volume of the main internal tanks has already been locked in via design as undersized to begin with.

Aux boosters add weight, but add thrust, which may be used to save fuel in main tanks (or achieve thrust levels over the ceiling capacity of the the main engines) while they are attached.

I see little reason to tie a booster's fuel source to the main tanks, personally.

The Aux Tanks each have their own rocket engines so don't add or subtract thrust into the core, unless SpaceX wants it to. (If the core is not built to tke it, don't futz the thrust. If it can, then maybe you use some extra thrust from the Aux Tank.)

Check out F9Heavy with the fuel crossfeed. This is that same technology but with smaller Aux Tanks. An F-9Extended, so to speak. If you look at the Wiki on the SpaceX launch fleet, you will see 3 versions of the F9v1.1. The third one carries a heavier load, but doesn't use the fly-back core. This would allow the core to fly back even with the heavier load.

[D Tibbets]

I think I know what KitemanSA is getting at. If you can lift the full core to a higher altitude and give it some downrange speed, you have an advantage. This is like the air launched Pegasus or Virgin Galactic Space Ship 2 (or is it 3?). He is separating the effort to get to that point and ignoring associated costs.
This is reasonable for subsequent considerations but indeed ignores the system costs to get to that point. The money cost of the extra tanks, with boosters, the cost to the thrust to weight equation (if any), the added complexity costs, higher risks, etc.

Space X has reduced launch costs, not by impressive rocket performance by a power perspective or ISP perspective, but by efficient manufacturing, simpler designs that are weight saving, and an overall business model that eliminates much of the waste of ULA. Further savings by recovery and recycling parts of the system has yet to be demonstrated. Potentially, perhaps as much as 25% additional savings is possible. But, it did not work out for the Shuttle SYSTEM. If Space X can pull it off. it is not only a demonstration of technical prowess, but a good business model- KISS.

The Falcon 9 heavy is basically what KitemenSA is describing. It will indeed increase payload to orbit, and increase leniency in booster recovery and possibly reuse. The questions are in the details of the technology and the total system considerations.

A possible comparison may illustrate my point. Hydrogen burning for cars may seem a great idea, no CO2, no petroleum use. It is the perfect fuel for everybody, especially those concerned about global warming. But, the press, and pundits generally ignore the system costs! How much money and energy cost does it take to produce the hydrogen. You cannot mine it directly. Like aluminum, it is useful, but it first has to be firstprocessed from oxides, and this requires a lot of energy (from coal, oil, nuclear, geothermal, solar, etc.). This is why aluminum costs more than iron. It costs more energy to make it into a useful form. Additional costs from hydrogen fuel is storage costs. It takes large tanks to store the gas, liquefaction costs a large amount of additional energy, and storing in metal hydrides costs energy too. Hydride storage is a technology that is not yet proven from both scientific and economic view points. Hydrogen is great, but only if the total system involving it's production, storage and use is a profitable one.

Dan Tibbets

[TDPerk]

"But, it did not work out for the Shuttle SYSTEM. "

A meaningless data point to regard, I think. The STS was designed to be partly expendable and partly remanufacturable, to be refueled and reflown. SpaceX rockets were designed to be refueled and reflown. To take SpaceX at its word concerning the recovered booster, it has achieve that.

[D Tibbets]

"But, it did not work out for the Shuttle SYSTEM. "

A meaningless data point to regard, I think. The STS was designed to be partly expendable and partly remanufacturable, to be refueled and reflown. SpaceX rockets were designed to be refueled and reflown. To take SpaceX at its word concerning the recovered booster, it has achieve that.

Almost, but not quite. One engine apparently suffered some ingestion damage. And of course, the first stage has not been reused.

From a system perspective, there is still much to be determined/ perfected. If only one in, for example, three boosters can be retrieved and reused several times before write off, does the cost of retrieval (both in cost in dollers and in cost in payload capacity) result in net gain? Dollar costs include additional cost for retrieval aspects of the rocket- landing legs and guide vanes, landing pads, cost of fuel (probably a very minor cost despite some claims by ULA), etc. Decisions to forgo retrieval if the weight of the payload is too high in some missions also eats into the final system balance. You spent a portion of the development and operational capacity without benefit in these cases. At some point between recovery success rate and extra associated costs there is a tipping point. I used one in three but I actually don't know necessary success rate. How close to 100% does it have to be? And, again, the Shuttle system had a very good reuse rate. It was the refurbishment/ preperation for reuse that was prohibitively expensive. The Space X business plan is to develop a system to avoid most of this second cost component. On paper it makes sense, actual accomplishment of this plan is still a work in progress. They have made progress towards their goals. They have also repeatedly demonstrated Murphy's Law...

Dan Tibbets

[TDPerk]

"the first stage has not been reused."

But it has been refueled and refired for a full duration burn. No anomalies were present in the combustion which would have shut it down.

I believe they are looking at whether post-landing processing caused the pressure anomalies or whether the landing did.