Discussion SpaceX's Grasshopper RLV

[Urwumpe]

Again, as said before ... There must not be a bad minimum thrust to weight. SpaceX uses pintle injectors, which are generally deep throttle capable. How much deep throttle is the question.

This relative heavy landing gear would weight about 10% of the landing mass. If it is without landing gear a typical rocket stage, its drymass would weight 8-10% of the total lift-off mass, so this one would be 9% to 11% drymass. Means it needs a throttle ratio between 1:12 and 1:15. Both is no big deal for pintle injectors.

So... I don't really understand the fuzz about "how clever their engine on strategy is".

They just limit gravity losses by having a short powerful burn at the end, then a weak but long burn, with a lot of fuel being used for compensating gravity.

 

[RGClark]

Again, as said before ... There must not be a bad minimum thrust to weight. SpaceX uses pintle injectors, which are generally deep throttle capable. How much deep throttle is the question.
This relative heavy landing gear would weight about 10% of the landing mass. If it is without landing gear a typical rocket stage, its drymass would weight 8-10% of the total lift-off mass, so this one would be 9% to 11% drymass. Means it needs a throttle ratio between 1:12 and 1:15. Both is no big deal for pintle injectors.
So... I don't really understand the fuzz about "how clever their engine on strategy is".
They just limit gravity losses by having a short powerful burn at the end, then a weak but long burn, with a lot of fuel being used for compensating gravity.

The only problem is SpaceX has given no indication the Merlin 1D can deeply throttle. It's only been cited as throttling down to 70%.

Bob Clark

 

[Urwumpe]

The only problem is SpaceX has given no indication the Merlin 1D can deeply throttle. It's only been cited as throttling down to 70%.

If you look at the broader picture, you should notice that SpaceX publishes nearly no technical data at all. They only say what the customer needs to know, and leave everything, that can be used by a rival company, secret.

So, it does throttle down to 70% during actual flight (MaxQ), but it does not say, how far it could throttle if needed.

Since it is gas-generator cycle, this could be very far. It is simpler to make a gas generator operate at lower mass flows, than a complex but more efficient engine, that requires on many different flow paths and heat exchangers... or worse of all even has phase changes (expander cycle, many injectors) or different phases mixed.

 

[Cairan]

I think they'll stick with the Merlin 1D for the first stage if it's simpler to throttle down, less things can go wrong on the first stage... The Merlin 2 (or Raptor) is not intended for that stage, in my opinion.

They are looking at staged combustion of LOX/methane for the Raptor engine, which in my mind sounds like a more efficient upper stage engine to maximize the ISP they get, gaining in terms of performance compared to LOX/kerosene for the upper stage but less than hydrogen... however, they don't have to put up with the hassles of an hydrogen tank.

 

[RGClark]

SpaceX says they will attempt a water landing of the first stage on the first test flight of the Falcon 9 v.1.1. They expect to have a working return to launch site version within a year:

Musk: SpaceX to Attempt Falcon 9 First Stage Water Landing
Posted by Doug Messier on March 28, 2013, at 1:50 pm in News
http://www.parabolicarc.com/2013/03/28/musk-spacex-to-attempt-falcon-9-first-stage-water-landing/

Bob Clark

 

[Urwumpe]

I have to quote something that should be interesting:

Musk said he expected to lose first stages during the initial recovery attempts. The company is looking to gain the experience and data needed to bring a first stage back to the launch site next year for a propulsive landing using retractable legs. He said that attempt could occur in mid-2014.

Remember, that SpaceX tried the same on the Falcon 1 and lost every first stage...

 

[MattBaker]

Remember, that SpaceX tried the same on the Falcon 1 and lost every first stage...

...and nearly had to abandon the project because no one wanted to invest in the crater-creator.

 

[Donamy]

More than a couple people here have had egg on thier faces, when it comes to doubting SpaceX.

 

[Urwumpe]

More than a couple people here have had egg on thier faces, when it comes to doubting SpaceX.

More than a couple people here also had been pretty right, when they pointed out, that Musks tweets are not changing physics.

 

[Donamy]

More than a couple people here also had been pretty right, when they pointed out, that Musks tweets are not changing physics.

Example ?

 

[Urwumpe]

Example ?

The whole Falcon 1 program - or better: SpaceX before NASA put tax payers money into it.

The Mars quote.

The manned capability, that is still years behind what said when the Dragon capsule was announced.

 

[Donamy]

The whole Falcon 1 program - or better: SpaceX before NASA put tax payers money into it.

The Mars quote.

The manned capability, that is still years behind what said when the Dragon capsule was announced.

I don't think they would have gotten funding if NASA didn't see potential in the design.

We're not talking about Mars.

I bet they get there, before anyone else (in the private sector).

 

[Urwumpe]

I don't think they would have gotten funding if NASA didn't see potential in the design.

They have received quite little funding per program for a company that already launches into space. But they have quickly adopted to the business model of Boeing and Lockheed - be everywhere where NASA offers money.

 

[Donamy]

Nothing wrong with that. IMHO

 

[Urwumpe]

Nothing wrong with that. IMHO

IMHO, you should at least then stopping bragging that you are the first private company. It maybe started that way, but today, it is not much different to Boeing, if you ignore the fact, that Boeing has no Elon Musk for annoucing new products and achievements, but a PR department, that is equally often wrong.

 

[RGClark]

Remember, that SpaceX tried the same on the Falcon 1 and lost every first stage...

I presume these water "landings" are going to use the techniques learned from the Grasshopper tests.

Bob Clark

 

[N_Molson]

IMHO, you should at least then stopping bragging that you are the first private company. It maybe started that way, but today, it is not much different to Boeing, if you ignore the fact, that Boeing has no Elon Musk for annoucing new products and achievements, but a PR department, that is equally often wrong.

At least a bit of reason in an insane world ! I couldn't say it better.

 

[Urwumpe]

I presume these water "landings" are going to use the techniques learned from the Grasshopper tests.

Bob Clark

Yes, but it is not happening under laboratory conditions, like the Grasshopper tests. In SpaceX view, it is a nice second use of the first stage after it has been used and would be just multi-million dollar junk.

But in my software developer view, I see that the software for doing this test will not be installed after separation. It has to be integrated into the normal flight software and be lurking in the memory of the guidance package during launch already.

Next, you will need to place a ship into the crash zone for getting the test data received via telemetry. If the crash happens beyond the horizon, you can't see it, and getting the data via TDRS would be much harder, unless you afford S-Band preamplifiers to improve the signal strength. Placing a ship into a rocket crash tone is pretty risky. Even the "illegal" junk collectors in Kazakhstan try to avoid being that close to the impact.

 

[Andy44]

Next, you will need to place a ship into the crash zone for getting the test data received via telemetry.

Or an airplane. Much larger horizon that way, and might even be cheaper than a ship.

It maybe started that way, but today, it is not much different to Boeing, if you ignore the fact, that Boeing has no Elon Musk for annoucing new products and achievements, but a PR department, that is equally often wrong.

I agree that SpaceX's "privateness" is overrated considering the only real customers for spaceflight are still governments. But I don't see Boeing doing this kind of RLV stuff.

Once was a time when the aerospace giants spent a lot of money out of pocket building and testing concepts with no firm contract or customer, simply betting that if they built something innovative the business would follow. The DC-X was the last time I can think of that happened, and that was at least 15 years ago.

SpaceX appears to be the only company doing this sort of thing anymore, mainly because of a charismatic founder with a vision. (Scaled Composites / Virgin Galactic perhaps being another example, driven by Rutan and Branson)

Even if it's a lot of glitz and PR, at least it gets people excited in space and technology again, so it's at least worth that. Plus it's fun to watch when they occassionally win one.

 

[DaveS]

Next, you will need to place a ship into the crash zone for getting the test data received via telemetry. If the crash happens beyond the horizon, you can't see it, and getting the data via TDRS would be much harder, unless you afford S-Band preamplifiers to improve the signal strength. Placing a ship into a rocket crash tone is pretty risky. Even the "illegal" junk collectors in Kazakhstan try to avoid being that close to the impact.

Have you really forgotten about the Space Shuttle so soon? The two SRB recovery ships R/V Liberty Star and R/V Freedom Star were not very far away from the predicted SRB splashdown sites, only 13 to 16 km distant.