Behind The Black Postings By Robert Zimmerman

SpaceX’s Grasshopper rocket successfully did a vertical take off and landing to a height of 130 feet last week. With video.

This is very cool engineering, but I remain skeptical any first stage rocket could carry enough fuel to both return to Earth vertically and also provide its payload enough thrust to get into orbit.

  1. Paul Lake says:

    I’m sure we both hope your skepticism will be proven unwarranted. A reusable launch system must be achieved to enable human settlement into space. Are there better ideas being worked on right now?

  2. A. Feit says:

    You’ve just got to run the numbers. Need more fuel, fly more strap-ons. They are reusable anyway. Who said 4, 6 or even 8 strap-ons are not viable? But like I said, you’ve got to run the numbers.

    • Hey, I hope you are right.

    • DougSpace says:

      Yes, and it would seem that one wouldn’t have to carry enough fuel to cancel all of the velocity, just enough to prevent too much heating on reentry, use parachutes to void much of the verticle velocity and then just a bit more at the very end. Perhaps this is why, in their reusability video they don’t show the first stage coming down to the cape but only the last portion (after the parachute disconnected).

      Also, initial reusability doesn’t have to be 100% in order to make a big difference. Even if only the first stage were reusable and if it didn’t cancel horizontal velocity but landed on a ship or an island, that would still significantly lower their launch costs and make them much more competitive than others. This would give them more time and money to perfect reusability further.

    • DougSpace says:

      Regarding strap-ons, if you use crossfeed, then the strap-ons will detach earlier and so require less fuel to cancel vertical velocity.

  3. wade says:

    isn’t This what von Braun and others designed back in the ’50s ? those designs proved to be too large to be cost efficient and were scrapped.

    • Tom Billings says:

      “isn’t This what von Braun and others designed back in the ’50s ? those designs proved to be too large to be cost efficient and were scrapped.”


      The stages of the launch vehicles of “Projekt Mars”, and other pre-sputnik proposals, were using different propellants, and were using wings to fly back into the atmosphere. They were hoping that enough wing surface could lower the heat load on the vehicle. It turned out that the wings that could do that enough were far too heavy, and the payload too small. In addition, the nitric acid oxidizer and hydrazine fuels were too corrosive on the one hand, and too poisonous on the other for continual rapid turnaround of vehicles.

      In addition, until Vostok1 flew, there was no money in either ABMA’s or later NASA’s budget to build anything like that, anyway.

      The vehicles cancelled in the Saturn program were steps between Saturn 1 and Saturn 5 that would push the Moon Landing back into the 1970s. Unfortunately, the Earth-Orbit Rendezvous techniques looked like they *might* do the same, and so they were cancelled as well. By the time Gemini 3 flew, Lunar Orbit Rendezvous was the assumed mode of flight.

  4. That is cool, but the coolest part of that video isn’t the engineering, it’s that it’s being done by private enterprise.

  5. Chris Kirkendall says:

    Well, obviously a lot to be worked out here, but at least it looks like the basic concept works. Whether it will become practical is another matter, but it’s great to see someone trying. Many things we can do today take for granted once looked impossible or impractical, but someone had the courage to dream & actually try…

  6. libs0n says:

    I’m just a layman, and I’m bound to be a bit wrong, but this is how I understand it.

    1. The first stage dry mass doesn’t go to orbit, just part of the way, that means only a small part of the deltav is proportioned to speed it up. That means it isn’t traveling as fast when it needs to be slowed down. It also means that additional mass added to the first stage for recovery doesn’t exact a full 1:1 payload costs, but something like 10 to 1, or adding 10 pounds to the mass of the first stage booster only costs 1 pound reduction in orbital payload.

    2. The first stage mass is mostly fuel. Once its burn is completed, the first stage is much much lighter, like only a few percent of the mass it was. It is basically an empty fuel tank. This is the dry mass. That means it costs much less in fuel to decelerate and land it. Using the estimated first stage mass figures at, a Falcon 9 weighs 419 tonnes at liftoff, but only 28 tonnes at burnout.

    The rocket is also very overpowered for that duty, since the engine thrust is sized to get the whole fueled rocket off the ground.

    So you are only returning a ~28 tonne mass(plus whatever recovery mass is necessary) to the ground, and the fuel and gear for that, as stated in point 1, doesn’t extract a full penalty from your orbital figures.

  7. wade says:

    i agree libs0n, and further, these are the concepts of rocketry long Before any space programs were even tried. watch an old space movie, for instance, the 1955 film ” the Conquest of Space” .

  8. Chris Kirkendall says:

    Re: The first stage mass is mostly fuel. Once its burn is completed, the first stage is much much lighter, like only a few percent of the mass it was…

    Right – good point…

  9. mpthompson says:

    I have to assume that the folks at SpaceX have run the numbers and the math works out with respect to having enough remaining fuel to slow and land a booster. If so, it then turns into an engineering effort to prove out the math. Something SpaceX seems to be making good progress on.

Website Maintained by Artist and Virginia Web Developer Leo Charre