SpaceX Grasshopper Test
There is an old saying, he bit off more than he could chew. This could be the case with the concept being explored by SpaceX and their new rocket technology. In the most recent test on March 4th they lifted the Grasshopper rocket 80.1 meters (262.8 feet), hovering for approximately 34 seconds. You can see the video of this test below.
While they may have the money to pull this demonstration flight off it is not clear the concept will work, or will be worth while. The ability to hover and land a rocket has been around for decades and while interesting and somewhat fun in a Buck Rogers sort of way it is actually not all that great of an idea. The fuel needed to land the rocket and the associated weight reduce the useful payload sent into space. Smaller payloads also mean more launches are needed to get a given mass to space, and therefore more risk of failure. In addition the likelihood of failure is increased. A rocket engine and the avionics needed to land are much more complex than a heat shield and a parachute. According to the SpaceX web site “the vast majority of launch vehicle failures in the past two decades can be attributed to three causes: engine, stage separation and, to a much lesser degree, avionics failures. An analysis of launch failure history between 1980 and 1999 by Aerospace Corporation showed that 91% of known failures can be attributed to those subsystems”. With that in mind 2 of the three major causes for launch failures would now also be involved in landing.
Video of the Falcon 9 reusable rocket concept.
“With Grasshopper, SpaceX engineers are testing the technology that would enable a launched rocket to land intact, rather than burning up upon reentry to the Earth’s atmosphere,” company officials stated after the rocket’s fourth test flight.
The concept is something like this. The rocket launches and the first stage drops off, the first stage engine then fires again and lands it gently, ready to be cycled for the next launch. The second stage then propels itself into space, delivers it’s payload, the returns back to Earth, first using a heat shield to decelerate and then slowing using the engine to land. Ready to be refurbished and reused. Seems like a great idea…until actual physics is involved. The reality is that the amount of fuel that is needed to be carried in order to accomplish is prohibitive. Think about it, all of the fuel needed to take off, and the return to Earth must be carried aboard the vehicle. The weight of all this fuel simply does not allow this concept to work…that is why it has never been done. NASA uses parachutes for a reason. Why use rockets and fuel for the first stage landing when a simple reliable parachute will work? They are cheap, simple, effective, and reliable. This is one time where NASA has embraced the KISS (Keep It Simple Stupid) principal. Maybe not so much by choice as by necessity. There really is no other solution that works with chemical rocket technology. If you notice the SpaceX video, the are using a chemical rocket. This method is also very complex, and complexity leads to failure.
For whiz bang SpaceX gets a 10 for their effort..for the actual applicability well, not so much. They should get a parachute and spend the money somewhere else.
This is written on the eve of first flight for Falcon 9R (Reuseable). SpaceX has dozens of flights on their books for the original Falcon 9 but it looks like they are planning to use an untested Falcon 9R for these. If Falcon 9R fails to deliver it’s cargo to orbit then they risk losing customers. Using original proven Falcon 9 to fill near term orders would seem safer especially with so many orders on their books. Here is hoping 1) Falcon 9R deliveries its cargo successfully and 2) the soft land on water works.
I’m not so sure that you are citing physics rather than accumulated prejudice. The Falcon return vehicle would only use one of the nine engines and have to land less than one ninth of the original weight. The current F9 Heavy has additional boosters with a 30 to 1 ratio of full to empty weight. In addition, the engine will only have to arrest a delta-V far less than the velocity originally achieved by that stage while boosting the entire rocket, first, second, and orbital payload. That should require far less than 10% of the original fuel load. If the full to empty ratio is anything like the cited one, the fuel required should be less than 5% of the original fuel load. Such a vehicle could eventually launch over land masses in a way we don’t currently permit It might be cheaper to return to another landing site on or close to the orbital path, but return to the launch site would be ideal for swift reuse.
Part of my point was that the fuel needed (%5-%10 by your estimate) is heavy and that will reduce the usable payload to orbit. So for arguments sake what would have taken 10 launches will now take 11 to get the same payload to orbit. Extra launch brings extra risk of faulure, not just of the rocket but also the payload.
In addition the fact the engine is needed to land also adds risk. The engine will be used more, cycled more, and this, in my opinion, will lead to a higher failure rate. You seem to know more about it what is the expected useful life of these engines? How many launches under this scenerio would they be able to support?
Yes I am using my “accumulated prejudice” in my analysis…some call “accumulated prejudice” experience.
As W. Edwards Deming often said, and I paraphrase, “experience is more often inchoate prejudice than it is actual knowledge.” As he brought the quality surge to U.S. industry after U.S. industry finally figured out that the Japanese were beating our brains out because they were listening to Deming, many did not get the message, and it is apparent that NASA was sometimes in the laggards after the early push to the Moon.
I suppose that pushing approximately 250,000 lbs into orbit with each shuttle flight, only to return close to 200,000 of it to Earth was a piece of brilliant engineering, and that is not to mention the tens of thousands of cubic meters of on orbit space that could have been made available by providing the slight extra push required to put the external tanks into orbit. In addition, wings on a vehicle that spends 99+% of it’s time in the vacuum of space seem more than a bit of a waste.
Now let me get to your specific points. It is hard to believe that you are carping about a less than 10% reduction in payload for the timely and easy reuse of the vehicle. And, the risk of failure will be less and less with time as the vehicle matures…and so far it is five for five. Also failure of the return to launch site does not equal loss of the mission. The F9 has nine engines and can make mission with only eight, as it has already proved. If the return of the vehicle does not happen, then that only represents additional cost, not loss of payload. With the use of the final form of the Dragon capsule, recovery of payload/occupants is possible at any point of the launch from zero to orbit.
It’s also hard to believe that a NASA type is talking about risk associated with engine reuse, apparently having forgotten about the SSME’s. And the SSME’s are far more complex and fragile than the LOX/kerosene engines on the F9. Also, before people are put on that torch, several hundred of those engines will have flown. Testing has been repeatedly done on F9 engines with total duration of more than ten full missions. What’s not to like. The 1D version of the engine has been flight qualified in the same manner, and it is both simpler and easier to manufacture as well as more efficient.
Why not give a cheer to someone who is attempting something new, at his own expense, no less.
First I think it is great they are trying something new…but NASA is kicking in some of the money it is not all on their own dime. Falcon-9 was significantly accelerated by the purchase of several demonstration flights by NASA. This started with seed money from the Commercial Orbital Transportation Services.
The Shuttle was designed by politics as much as engineers which is why it was the way it was. No crew escape method, a totally unrealistic advertised turn around time, a totally unrealistic proposed budget per flight, and the reliability that was required/advertised of a manned spacecraft was clearly not met. I never said the shuttle was a great idea either. It was an amazing piece of engineering. I witnessed several launches myself and it was impressive, but it was not what I think the engineers of the time would have designed if they we left to design it without the politics and spin.
Even SpaceX acknowledges how hard what they are attempting to do is stating “[They] expect several failures before they learn how to do it right”. I hope they do learn to do it right, maybe they will. I just seems that there are many risks. Reusing the rockets and reconditioning them between flights is never as cheap or easy as is ever advertised. Having seen this kind of thing before it was always more hype than reality. Time will tell.
It is not that I am such a fan of SpaceX, but that I am convinced and have been for decades that we must get off this cosmic bullseye if we are to survive as a species. That is similar, but not identical to the sentiments expressed by Musk. He wants to go to Mars, which I regard as just another gravity well/trap. It certainly is a bit easier to depart than Earth, but in some ways it is much harder on which to land. It is the only planetary body easily accessible to us that could easily support a space elevator, to the top of Oympus Mons.
All that aside, even if the F9 and F9H never become fully reusable, they are already far cheaper than any other rockets in use or even promised for the moment. While NASA did provide access to technical information and seed money in the form of contracts for deliverables, NASA received in return ISS trips at a fixed price lower than any others yet even proposed. After the huge subsidies provided by both DOD and NASA to many other companies, sometimes only to “guarantee” capacity, it seems a bit rich to talk of subsidies to SpaceX. The carping about SpaceX, I believe, is largely due to the fact that they have delivered largely what they promised at a fixed price, and the number of commercial contracts largely supports that view.
At the moment, I see no other means of achieving orbit that will be substantially more cost efficient than what SpaceX is doing. It reminds me of the earlier proposals for BDB’s, updated with more modern materials and simplifications of more modern technology all wrapped into relatively mass production. The flexibility of the overall design has been shown by the rapidity with which the engine configuration of the F9 core was changed from 3×3 to octal and one. Reusability would be the cherry on that confection.
The thing most likely to damage SpaceX is success rather than failure, as in the case of so many dotcoms of the past decade or three. If they cannot maintain a sufficient launch rate and success ratio to satisfy their customers, those contracts will leak away to others or the contracting companies will collapse due to delays in their business plans.
For my purposes and goals, SpaceX offers the only likely affordable means to be available in the next decade. SLS will fail to be affordable within the budgets that will be available, and it really has little or no role in a sustainable occupation of space; spectacular one-offs, yes, sustainable occupation, no.
As I noted above, Mars is a chimera, a mirage, at least for the next 2-3 decades, but Musk appears set on expending his energy on it. The folks talking about mining asteroids have the right idea, but the wrong approach, and no likely source of boost. They want to go out to asteroids and send back what they harvest from deep space. This is short-sighted in more ways than one. The risks are high and the loss of an effort is a total loss. Moving small asteroids into Earth and/or Lunar orbit, harvesting from them, and using them as permanent, safe bases will carry us forward into the future we seek.
I relly like the fact that a private company is making such great strides in space technology. We needed NASA and the government to pave the way, and still do, but private inovation and money are the real key to the future. Spain had to fund the first voyage to the new Americas, and that investment lead to where we are today. You go SpaceX!!!