SpaceX Grasshopper and re-usable plans

[sojourner]

Elon has actually referred to it as F9r.

[bigdad84]

They test fired the engines. engines burn RP-1 which is very sooty.

So, everytime they land a stage back at the launchpad (Assuming they can) it's going to be covered in this black soot?

[sojourner]

So, everytime they land a stage back at the launchpad (Assuming they can) it's going to be covered in this black soot?

Probably not so thick. a static fire on the pad is going to leave more residue than a stage coming in to land.

[Superluminaut]

Probably not so thick. a static fire on the pad is going to leave more residue than a stage coming in to land.

Any chance you could stroll up to the people working the rig and asking about the schedule?

[nhnifong]

Why does the F9 burn RP1 anyways? it doesn't have as high an energy density as LH2, and it's dirty. Is it because of cost or because they can produce more thrust with it?

[NGTOne]

Why does the F9 burn RP1 anyways? it doesn't have as high an energy density as LH2, and it's dirty. Is it because of cost or because they can produce more thrust with it?

It's way denser, and MUCH safer. It's stable at room temperature, and doesn't tend towards exploding with little provocation. And you can get a lot more bang out of the same-sized tank (or the same bang out of a much smaller tank).

[fireflower]

So, everytime they land a stage back at the launchpad (Assuming they can) it's going to be covered in this black soot?

SpaceX is replacing RP1 with clean-burning LNG. (Liquified Natural Gas, also known as methane, or CH4.) It's exhaust is just steam and CO2. Their in-development LNG/LOX motor is called "Raptor." LNG has higher specific energy, higher exhaust velocity, higher oxidizer ratio, and slightly less energy density than RP1. The only reason RP1 was developed as a fuel instead of using LNG was a military decision before NASA existed. Since Goddard, American rockets had used petroleum-based fuel propellants. There was already a supply chain for it. However there is no such petroleum infrastructure on Mars, whereas methane can be synthesized from the ambient atmosphere. Russia, China, and NASA are all trying to develop a rocket motor that uses it. Compare and contrast:

RP1

Boiling point: 420 K

Specific energy: 42.8 MJ/kg

Energy density: 33 MJ/L

Exhaust velocity: 3510 m/s

Oxidizer ratio: 2.77

LNG

Boiling point: 109 K

Specific energy: 53.6 MJ/kg

Energy density: 22.2 MJ/L

Exhaust velocity: 3615 m/s

Oxidizer ratio: 3.45

LH2

Boiling point: 20 K

Specific energy: 141.86 MJ/kg

Energy density: 8.491 MJ/L

Exhaust velocity: 4462 m/s

Oxidizer ratio: 4.83

It's the Mario of bipropellants. Neither best vac nor atm but good all-around with perqs like no boil-off, modest cryogenic, easily synthesized, abundant throughout the universe.

Why does the F9 burn RP1 anyways? it doesn't have as high an energy density as LH2, and it's dirty. Is it because of cost or because they can produce more thrust with it?

You mean "specific energy." LH2 has a much higher specific energy. It's energy density is tiny, and energy density is more important in a first-stage engine than ISP. LH2 has such low energy density, and RP1 (and LNG for that matter) have such high energy density, they can store a lot more energy in the same volume pressure-vessel. At a certain point, the size of the vessel necessary to store the same mass of LH2 fuel literally outweighs the gain in exhaust velocity. You also have issues with LH2 being kept at 20 K and being so lightweight they "boil off" from whatever pressure-vessel you put them in. That is why many rockets use RP1/LOX first-stage and LH2/LOX second stage.

You can look at the math in this NASA study. It is about energy density of propellant and its effect on the payload mass fraction of the rocket being just as important as the exhaust velocity of the propellant. Specifically, it's about tripropellants, which is a wonderful way of explaining how important energy density is, because both ISP and energy density are taken to extremes in tripropellant rockets. It's got math, derivation, porkchops, and is readable. Fascinating stuff, like how adding aluminum to LH2/LOX rockets increases ISP but decreases payload mass fraction because adding aluminum precipitously decreases energy density.

Edited February 6, 2014 by fireflower
merged posts

[Kryten]

To clarify, they're replacing RP-1 with LNG for the upper stage only, as it has energy-density advantages and requires less specialised infrastructure than LH2 . RP-1 is still being used on the first stage, due to the high density allowing higher mass ratio, and energy density being relatively less important.

[fireflower]

To clarify, they're replacing RP-1 with LNG for the upper stage only, as it has energy-density advantages and requires less specialised infrastructure than LH2 . RP-1 is still being used on the first stage, due to the high density allowing higher mass ratio, and energy density being relatively less important.

"Four times the thrust of the Merlin 1D vacuum engine."

"Public information released in November 2012 indicates that SpaceX may have a family of Raptor-designated rocket engines in mind."

"Design thrust of the Raptor engine: 2.94 meganewtons."

I don't trust the press to report anything, let alone rocket science. From what they have reported SpaceX representatives as saying, and the nature of the fuel they're dealing with, it looks like they're replacing RP1 entirely.

EDIT: RP1 is dirty. If the spacecraft and the launch site look sooty, imagine what the inside of the motor looks like. LNG technically doesn't have a carbon chain, as it's just the one atom. For reusability they're going to have to switch to a clean-burning fuel, not a postwar relic from before we figured out cryogenics.

Edited February 6, 2014 by fireflower

[sojourner]

To clarify, they're replacing RP-1 with LNG for the upper stage only, as it has energy-density advantages and requires less specialised infrastructure than LH2 . RP-1 is still being used on the first stage, due to the high density allowing higher mass ratio, and energy density being relatively less important.

To further clarify, SpaceX hasn't actually said Raptor will be used in conjunction with Falcon 9 at all. The most we know about Raptor is that it is in development. Their exact plans for it are unknown. It's all pure conjecture at this point.

[Psycix]

Another great reason to use methane is the fact that it is possible to create methane on Mars.

[metaphor]

Since Raptor has about 3 MN of thrust, it would be way too overpowered to use on a Falcon 9 or Heavy upper stage. So unless they're developing an entirely new lower-thrust methane equivalent of the Merlin 1D, the Falcon series of spacecraft (Falcon 9, Falcon Heavy) will be using RP-1 for the foreseeable future.

The Raptor will probably be used for another series of larger methane-using rockets. Something like the Raptor 9 (same design as Falcon 9 but with 9 Raptor engines) would get about 60 tons to orbit, and a Raptor Heavy would get about 200 tons to orbit.

[jfull]

Wait, my thread got stickied?

Neat I guess

[sgt_flyer]

Another interest with combining LNG with LOX, is they are very close in terms of liquid state temperatures - much closer than lh2 and lox, so you will require much less insulation (even between the tanks themselves, as is lh2 kept cold enough to freeze the oxygen into solid state, which will allow to lower the dry mass.

[Spica]

To elaborate further on the dirtiness of RP1, I have been to the huntsville space and rocket center, and have been in the same room as an F1 that has been test fired. It burns RP1 and lox, and the room does NOT smell good at first, but then you get used to the smell of burnt parts of gasoline molecules. NOT that RP1 is bad though. It is only quite dirty.

[Exoscientist]

Since Raptor has about 3 MN of thrust, it would be way too overpowered to use on a Falcon 9 or Heavy upper stage. So unless they're developing an entirely new lower-thrust methane equivalent of the Merlin 1D, the Falcon series of spacecraft (Falcon 9, Falcon Heavy) will be using RP-1 for the foreseeable future.

The Raptor will probably be used for another series of larger methane-using rockets. Something like the Raptor 9 (same design as Falcon 9 but with 9 Raptor engines) would get about 60 tons to orbit, and a Raptor Heavy would get about 200 tons to orbit.

The Raptor could still be used on a Falcon 9 sized vehicle. You would simply use fewer engines. Probably also call it something else then.

Bob Clark

[Exoscientist]

...

You always read things like "private compagnies always work better than public organisations" but nobody is ever showing evidences of this. It is liberal ideology.

...

Not to be derailed into politics but that's actually a conservative viewpoint, at least as such terms are used in the U.S.

Bob Clark

[Exoscientist]

You've misinterpreted that statement quite badly, but that's to be expected given it's been taken out of it's original context. Here's the first version of it here;

Which I pretty much just paraphrased from this post;

which was incidentally made by this fellow. Given his experience in the area, it's pretty reasonable to assume he knows what he's talking about.

The problem with that argument is National Security satellites are so hugely expensive, frequently in the billion dollar range. NASA science satellites are also frequently expensive, such as the billion dollar Curiosity mission.

Commercial satellites in contrast are frequently in the $100 to $200 million dollar range. Imagine then the improvement to the satellite operators bottom line if they could reduce their launch costs from say $50 million to $5 million.

Just the current lowered prices of SpaceX without reusability led some satellite operators to be highly positive towards the change:

SES and SpaceX: Shaking the Industry to its Roots.

By Veronica Magan | January 21, 2014 | Europe, Launch, North America, Publications, Regional, Telecom, Via Satellite

Quote:

“This launch, in my opinion, is probably the most important launch in the commercial arena, certainly since 1996, no doubt about it,†Halliwell said. “There are detractors, who are hoping for a failure, but the majority of the commercial satellite world is waiting for a success because it really opens a whole bunch of opportunities.â€Â

...

The successful SES 8 launch is likely to mark a new era for the satellite industry. “The entry of SpaceX into the commercial market is a game changer, it’s going to really shake the industry to its roots,†Halliwell said. “We think this is the way to go forward for the future.â€Â

http://www.satellitetoday.com/publications/2014/01/21/ses-ans-spacex-shaking-the-industry-to-its-roots/

Bob Clark

Edited February 9, 2014 by Exoscientist

[sojourner]

The Raptor could still be used on a Falcon 9 sized vehicle. You would simply use fewer engines. Probably also call it something else then.

Bob Clark

Not if you still want it to be reusable. A raptor engine would provide too much thrust to allow landing. Unlike KSP, real rocket engines can only throttle in a narrow range of about %70 to %100. At %70 a raptor would still be providing enough thrust to lift the Falcon first stage off the ground.

[Exoscientist]

Not if you still want it to be reusable. A raptor engine would provide too much thrust to allow landing. Unlike KSP, real rocket engines can only throttle in a narrow range of about %70 to %100. At %70 a raptor would still be providing enough thrust to lift the Falcon first stage off the ground.

That hovering question has been much discussed on Nasaspaceflight.com. Even the current F9 has too much thrust just firing a single throttled down Merlin to hover. Apparently SpaceX will accomplish the landing doing short bursts of the engine.

Bob Clark

[Exoscientist]

First pics of Grasshopper-2.

Anybody with image processing knowledge to tease out more detail of that image of the base of the F9R? Much discussed whether it will have the full 9 engines or just three on this test vehicle.

Bob Clark

[Psycix]

If firing a single engine provides too much thrust, landing is still a possibility using a suicide burn.

[H2O.]

Not to be derailed into politics but that's actually a conservative viewpoint, at least as such terms are used in the U.S.

Bob Clark

Here in France, "liberal" is the word for "conservative" (at least in the economical sense of the term). So I mixed-up the terms, sorry. I wanted to say that there is no essential reasons for a private compagny to be better than a public agency.

SpaceX can be better, not because it is private, but because it comes after nationnal space agencies. It can make an evaluation about what agencies have done right and what they have done wrong, and think of a business plan according to that. Nasa did not have those kind of luxuries when it started.

Edited February 10, 2014 by H2O.

[kujuman]

Re: the soot from RP-1, is this soot deposited through the burning, or does it only really present itself at engine start/cutoff as unburned propellant is floating around? Secondly, is soot build-up a substantial problem in the "working parts" of the engine or just in the nozzle/outside?

With regard to the "too much thrust to land" discussion, the only time I can imagine one would want ~1g of acceleration for a lander is during the last few meters of descent (to allow some margin in your burn) as you need the vehicle to slow down before that, so more than 1g of acceleration, and at least as fuel is concerned, the higher the acceleration the better.

I wanted to say that there is no essential reasons for a private compagny to be better than a public agency.

In an ideal world, I'd agree, but at least experience with NASA doesn't seem to support this. Many of the "poor" decisions made by NASA are a result of having to deal with many varied stakeholders. With the Space Shuttle, it's widely believed that the military's requirements were at odds with the "civilian" requirements, leading to a less than optimal vehicle. In designing the SLS, NASA was constrained from day 1 by the political decision to use Shuttle derived hardware (presumably to help keep politically connected companies in business). I don't know how other space agencies operate, but I imagine there is still sacrifice of optimal vehicle design to answer political questions. So at least in this regard, SpaceX having better control over their own processes and decisions will give them an edge.

[Brotoro]

Re: the soot from RP-1, is this soot deposited through the burning, or does it only really present itself at engine start/cutoff as unburned propellant is floating around? Secondly, is soot build-up a substantial problem in the "working parts" of the engine or just in the nozzle/outside?

I was under the impression that soot would not form from burning RP-1 at the chamber pressures used in Space-X's engines... So I would guess it occurs at startup and shutdown.

Also, the soot from burning RP-1 can be beneficial to a rocket engine because the layer of soot inside acts as a substantial insulating layer to protect the nozzle walls.