Slashdot Mirror
The Grasshopper Can Fly Sideways
Phoghat writes "I'm of a 'certain age' and as a child grew up watching shows like "Rocky Jones, Space Ranger and others popular at the dawn of the space age. They always showed rocket ships sitting on their tails and blasting off, and landing, straight up. The shuttle went up that way but had to land like a plane, and anything else was considered impossible or impractical. Now, the Space X's rocket Grasshopper can not only do that, but has demonstrated sideways flight also."
I almost called dupe from SpaceX Grasshopper Launch Filmed From Drone Helicopter but this is new stuff.
I am Slashdot. Are you Slashdot as well?
XKCD just covered this! Good timing for the question.
TL;DR: Heat shields aren't going away because they are efficient.
And a rocket's motor is at the back. Of course it is going to point down to counteract. No matter which way you point the rocket, the motor must point mostly down.
One the one hand, this is a big step for SpaceX in developing a reuseable rocket booster. Kudos.
On the other hand; been there, done that.
When I see vertical-takeoff-vertical-landing my first thought is Armadillo Aerospace and their years of work on those rockets. Now that Armadillo is largely mothballed, have some of their guys turned up at SpaceX?
Never approach a vast undertaking with a half-vast plan.
The Space shuttle can fly in over a thousand different directions -at the same time- if its heat shield is damaged.
Sig Follows: "Suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself." -- Mark Twain
Aren't we all?
Diverts like this are an important part of the trajectory in order to land the rocket precisely back at the launch site after re-entering from space at hypersonic velocity."
While watching the video, I just imagined the "gas" gauge needle sinking fast to 'E'.
Having to carry all the extra fuel to land like that is going to drastically reduce the payload.
That's why space missions usually land some other way - parachute, blow up balls, crash land, etc ... more room for equipment.
rockets going sideways is not that new
But the stuff he is doing has been done before and doesn't actually answer a lot of the questions required for re-usability.
http://www.youtube.com/watch?v=JzXcTFfV3Ls
That's the DCXA and is a SSTO (Single Stage To Orbit).
Here is the BIG questions:
1) How big will it need to be to carry enough fuel to push something to NEO and come back.
2) How do you de-couple upper stages from it? You're going to be constantly burning, You'll need to turn off the rocket, or fire retro-grade rockets to slow it down so that the upper stages can de-couple.
3) Where do you launch/land from? You either need a huge area to cover (Calif to FL) or Lots of fuel to make the return trip.
Heat shields are the efficient way to slow from orbital speeds for reentry (e.g. the Shuttle), but conveniently for recovery the first stage isn't orbital. Grasshopper is basically a modified Falcon 9 first stage, and the goal of the testing is recovery of the first stage of Falcon 9-R, which is much easier than reentry from orbit..
We're not talking single stage to orbit here, and recovery of the second stage would certainly involve a heat shield. The first stage is a different animal. SpaceX seems to be intending to use a boost-back trajectory concept. I look forward to seeing how that works. (The controlled water "landing" attempt will be something to see, too, of course.)
The moon has considerably less gravity and atmosphere to worry about for VTOL. So if it's practical on the moon in 1969, it's reasonable it would take the better part of a century to become practical on Earth given that rocket technology hasn't changed that drastically since the Nazis were launching V-2s (or depending on how you define drastically, since the Chinese were launching emperors, see Wan Hu).
Hi, my name is Shavano and I know not what I speak of.
They always showed rocket ships sitting on their tails and blasting off, and landing, straight up[1]. The shuttle went up that way but had to land like a plane[2], and anything else[3] was considered impossible or impractical. Now, the Space X's rocket Grasshopper can not only do that
Do what?
systemd is Roko's Basilisk.
Is he the Wan Hu was legendarily blew himself up with rockets?
Am i the only one who wondered when the summary was going to get to something relevant to entomology? I was really baffled. I didn't know what rockets had to do with bugs :/
bad comparison. the LM actually operated in reverse. it landed at a site, then took off. that is very different from taking off and then landing back at that exact same site. furthermore, the part that took off was a totally seperate piece with its own rocket engine, so technically it was two craft (or two stages) performing two seperate operations, not one craft performing both. the grasshopper is also far far larger than the LM, and exercising greater degree of control and precision in a heaver gravity and different atmosphere.
and while you alude to the crew capsules landing without fuel, the current crop of LAUNCHERS in use, are disposable single use entities, which means you apparently missed the entire point of this experimental rocket is to validate the concept of a reusable launcher, which would dramatically reduce costs.
short version: shutup
The guy who said the election was rigged won the presidency with the second-most votes.
stuff that's been done decades ago? I don't have a clue as to why rocketing up the fuel you need to hover back down is supposed to be good, though.
it's not like it's rocket science...
The Grasshopper Flies, Heavy, Man!
burbleburbleburble...
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
The part that landed the LM was left on the moon.
Tony Stark has been doing this for 50 years.
http://alternatives.rzero.com/
Am i the only one who wondered when parent poster was going to get to something relevant to walking trees? I was really baffled. I didn't know what Ents had to do with bugs.
Am i the only one who wondered when the quoted text was going to get to something relevant to recursion? I was really baffled. I didn't know walking a tree had nothing to do with bugs.
Am i the only one who wondered why the quotes were forming some strange iterative behavior? I was really baffled. I didn't know why the stack trace was missing several parent posters; Probably -O dead code elimination, self referential side effect, or a GOTO bug.
I post therefore I was.
I always found this video to be impressive. It's a little scary in a terminator sort of way too.
We used to call it "thrust vector control". I worked in the Morton-Thiokol TVC lab for a while. The video shows a really excellent example of the technique, which is not new or controversial.
You can do TVC with hydraulics (heavy, but parts are easy to source and last longer) but you'll get better impulse numbers for the vehicle as a whole if you can divert some proportion of the pressure from the combustion chamber into mechanical actuators that change the direction the nozzles are physically pointing. With multi-nozzled rocket motors (regardless of whether they have multiple combustion chambers or not) you can point some thrust down and some to the side (which appears to be happening in the video) and get this kind of behavior.
Similar things can be done with moving vanes in the exhaust plume, but those will erode even faster than the mechanism described above, and will be far slower to change the thrust vector. Erosion of parts that have high pressure hot gasses flowing through them is a huge issue in rocketry, although fairly well understood at this point. External aerodynamic vanes like the space shuttle's wings will obviously work too, and won't erode much (during liftoff) but they are also slow and clumsy.
When I say the technique's not new, I do not mean to denigrate the achievement. I can confidently state that it's really, really hard to do it as well as is being shown in this video. I would love to be able to work with these guys, because they are clearly just full of the right stuff.
Another alternative system to TVC is separately fueled ACMs - Attitude Control Motors - such as vernier thrusters or the solid fuel ACMs on hypersonic crusie missiles. When you use gimballed nozzles to achieve TVC, though, you can potentially have the entire force of the main thrusters available for attitude control, and the fuel delivery system can be much more concentrated and simple.
Graphical overview of the common methods of TVC here
Am I the only one who clicked through to this while scanning headlines, thinking it referred to living creatures?
"No matter how cynical you get, it is impossible to keep up." -- Lily Tomlin
I was doing this in arcades in the 80's.
The Delta Clipper (Experimental) did this about twenty years ago.
It is pretty awsome watching a rocket lift off, stop dead a few hundred feet up, move sideways a few hundred feet, and then descend to a landing. But it has been done.
That said, kudos to Space X for doing it with their own vehicle.
-- Alastair
The controlled burn decent shown in the video looks impressive but will always be impractical from a financial perspective.
In fact, it is the most horrific way to land a rocket coming from space due to the amount of fuel that would need to be used to decelerate it. We use parachutes or wings to slow things down for landing in an atmospheric environment because it saves a lot of energy compared to doing a direct burn for deceleration.
Essentially, you have to use at least as much fuel as you needed to get the return payload up in the first place. Then remember that you need to also use extra fuel on the ascent to lift all that extra fuel that you need for the descent! Compare this to a heat-shield/parachute re-entry where you use almost no fuel.
Thus, this technique will only be useful for landing in places with no atmosphere or as a final descent stage after using some other method to slow the rocket down from the hypersonic re-entry velocity. Also remember that the Eagle lunar landing module did everything shown in that youtube video back in 1969.
The moon has considerably less gravity and atmosphere to worry about for VTOL. So if it's practical on the moon in 1969, it's reasonable it would take the better part of a century to become practical on Earth
Ok, look at the videos of the tests of the moon landers and systems here on earth ... under our own gravity.
You are correct that rocket tech really hasn't changed, yet somehow you think today we can do it but back then we couldn't?
Your post is utterly conflicted.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
John Oliver has a few words for you
I came here expecting to see some new discovery about insects.
Rocky Jones. Gimme a break.
Well, it's certainly cheaper than having some internet billionaire salvage your rocket parts off the sea floor for you.
Of course with precedents like Howard Hughes, the Glomar Explorer and project Jennifer and Robert Ballard finding the Titanic while secretly researching the Scorpion & Thresher wrecks , it leads one to wonder what internet billionaire Jeff Bezos is really up to.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
Is anybody else disappointed that TFA doesn't have slow-motion video of an actual grasshopper (the insect) flying sideways? That'd be pretty cool.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
My post makes a few points, but I don't see the conflict.
1) Rocket tech hasn't changed much. This, we agreed on.
2) It was practical to do it that way on the moon in 1969.
3) It has not been practical to do it on Earth up to this point.
4) The main difference in practicality between Earth and the moon has to do with atmosphere (or lack thereof) and gravity.
Don't confuse practical with possible. I never said we couldn't do it on Earth, just that we've had better ways due to the slow evolution of rocket technology and that might finally be changing.
The space shuttle and NASA and Russian landing capsules land using no fuel. Beat that, Space X.
None of those have recoverable first stages; the shuttle might have been much cheaper to fly if the booster rockets were reusabe. Did you not even read the fucking SUMMARY??
Using the same engine, rather than treating the engine as a disposable object that only performs one burn in its lifetime. Most rocket engines can't be throttled, can't be shut down and then restarted in flight or otherwise.
The tricky part is going to be for any stage to have enough delta-V to return to the pad after lifting a payload to orbit. Also, as far as I can tell, this takes a drag chute for lower stages, and a re-entry shield for upper ones.
Bruce
Bruce Perens.
How about the Moon and Mars? It seems to me that the fuel capacity of Dragon isn't enough to do both lunar descent and ascent just on the Super Draco thrusters and the trunk's fuel capacity.
Bruce Perens.
What a shock, another article on Slashdot fellating Elon Musk for his many AMAAAAAAAAZING SCIENCE ACCOMPLISHMENTS!
Did he buy a controlling interest in Dice.com or something?
Fuck.
This is a nice step in Musk's plans to make the 1st stage of Falcon 9 re-usable... but before people swoon over this apparent realization of SciFi fantasy and start talking of warp drives and teleporters, a few points are in order:
1. This has been demonstrated before by several other teams (DC-X being most famous, and Amazon's Jeff Bezos, with his Blue Origin vehicle, being hardly noticed). The thing the grasshopper demonstrates is not that the general concept works, but rather that Musk's team has mastered it and, more importantly, done it with an actual first stage of an actual launch vehicle (this part is the unique, and very cool part)
2. This is not proof that winged space planes (like the shuttle) or lifting bodies (like SNC's Dreamchaser) are obsolete or a dead-end. Musk is planning to use a small quantity of residual first stage propellant to land an otherwise-empty first stage for re-use; the scheme would fail if there was any added mass (like a payload). Shuttles brought tons of payload back to Earth to a gentle runway landing, and lifting bodies are similarly tasked with returning payloads. (yes, I know, Musk plans a propulsive landing for his manned capsules... but that's NOT what grasshopper demonstrates and that's a subject for a different discussion as there are many substantive differences, though this experience will certainly pave the way for that effort)
3. The fact that this one technique (of balancing a tall empty beer can on a pillar of fire and steering it around before landing it) is being demonstrated in the real world does not automatically prove that any other dreams of Roddenberry, Heinlein, Asimov, etc are any more practical or likely to appear in the near future than they were two years ago
Well done, Space-X, keep it up!
The scale of things here is something to point out. The LEM was just 18 feet tall, where as the Grasshopper was a full 10 stories tall (a little over 100 feet). That much larger size has many more problems that need to be addressed as not everything scales upward as just simply larger parts on everything. Quite often things that work on a scale model simply won't work on a larger version of the idea.
As far as why this wasn't done in 1969 but can be done today, it is missing that a whole lot of technological progress has happened in the meantime. I agree with you that it has take time to develop things like guidance computers which weigh as much as a mouse along with some significant progress in materials science that has allowed for some of the current generation of rockets to be developed. Simply put, the Grasshopper couldn't have been built much earlier.
No wonder Kwai Chang Cane had a hard time catching one.
Tracy Johnson
Old fashioned text games hosted below:
http://empire.openmpe.com/
BT