With a 400 Isp engine, one percent of the vehicle landing mass can kill 40m/s of velocity. That is over 80 mph, which an efficient VTVL vehicle could expect to have as its terminal velocity.
A parachute masses more than 1% of its load.
There are lots of other factors that can push the decision either way, but it is certainly within the realm of feasible engineering decision.
Yes, this is very similar to what I am working on.
www.armadilloaerospace.com
Their current vehicle is a good deal larger than ours, has an aeroshell, and significantly, uses liquid hydrogen / liquid oxygen, a much more potent and difficult propellant than the hydrogen peroxide we use.
On the other hand, my project has been a lot faster and cheaper. I have spent about $50k and we have been working on it for nine months, versus their $400k and four years.
Our first up scale vehicle is going to be ready in a few months. It won't go very high or fast, but we can carry a person on it...
Next year, at the very least, we will have a supersonic manned rocket ship.
It is easier to get a high thrust to weight ratio out of solids, even though they have a lower Isp and generally a lower total dV per stage.
To get more thrust out of a solid, you basically just need a bigger nozzle, while to get more out of a conventional liquid engine, you need a bigger nozzle, and bigger turbopumps, plumbing, and combustion chamber.
Not that I think solids on a manned vehicle are very sensible...
We will have a manned rocket vehicle flying by the end of the year, but it will be a modest little thing. The performance will only be about what you got out of the old Bell rocket pack, but it is fully fly-by-wire (and can be tested remotely) with active stabilization, and all the subsystems are directly scaleable to much larger vehicles.
I will probably enter as an X-Prize competitor at that point.
I don't put a lot of stock in pinning down "firsts", even though people in general, and the media in particular, love to harp on it.
Everything is built on past work.
A lot of people like to think of creativity and innovation as something that springs from the void, but the truth is that everything is traceable to its origins.
I consider myself fortunate that I am consciously aware of the process. I can dissect all of my good ideas into their original parts, and even when there is an interesting synthesis, the transformation can usually be posed as an analogy to some previous work.
Given that fact, you will rarely find me touting anything as a "first", because I could always say it is "sort of like this thing over here, but with the principle demonstrated by this over there added to allow it to give the feature we wanted back then" and so on.
There are the occasional "eureka!" moments, but they tend to be in twitchy little technical things, not the larger ideas like "3D environment" or "multiplayer gaming".
I'm not all that concerned with our place in history. The process has been interesting enough in its own right, and lots of people have enjoyed the work as we produced it.
The FAA regs (FAR 101) used for model/high power rocketry specifically refer to "unmanned rockets", not "unpiloted rockets", so it isn't at all clear how something like this is regulated.
I have sent a query to the FAA about getting waivers for the manned rockets my team is working on, but it got booted up to Washington a couple weeks ago, and I haven't heard back yet.
I wind up doing my own internal PPC vs X86 benchmarks almost every year.
I'll set up whatever current game I am working on to run with the graphics stubbed out so it is strictly a CPU load. We just did this recently while putting the DOOM demo together for MacWorld Tokyo.
I'll port long-run time off line utilities.
I'll sometimes write some synthetic benchmarks.
Now understand that I LIKE Apple hardware from a systems standpoint (every time I have to open up a stupid PC case, I think about the Apple G3/G4 cases) , and I generally support Apple, but every test I have ever done has had x86 hardware outperforming PPC hardware.
Not necessarily by huge margins, but pretty conclusively.
Yes, I have used the Mr. C compiler and tried all the optimization options.
Altivec is nice and easy to program for, but in most cases it is going to be held up because the memory subsystems on PPC systems aren't as good as on the PC.
Some operations in Premier or Photoshop are definitely a lot faster on macs, and I would be very curious to see the respective implementations on PPC and X86. They damn sure won't just be the same C code compiled on both platforms, and it may just be a case of lots of hand optimized code competing against poorer implementations. I would like to see a Michael Abrash or Terje Mathison take the x86 SSE implementation head to head with the AltiVec implementation. That would make a great magazine article.
I'll be right there trumpeting it when I get a Mac that runs my tests faster than any x86 hardware, but it hasn't happened yet. This is about measurements, not tribal identity, but some people always wind up being deeply offended by it...
I should mention that really, all of this work can be traced back to slashdot.
Until a year and a half ago, I hadn't thought about space and (real) rockets since I was a kid.
I started reading slashdot for the open source coverage, but the occasional space story and the comments on them led me to the CATS prize and the other things going on in the space community.
I spent a year learning the engineering aspects and funding a few things that I considered interesting (JP Aerospace, SORAC, Space Frontier Foundation, and XCOR), and the last six months actually doing something myself.
I was sort of planning on submitting an article about the whole process at some point, but it looks like I got preempted (and our site is slashdotted)...
The throttle is manual, but attitude control is computer managed. The joystick input gives a target angle, and the computer deals with rates and pulses to try and get it there. Manual control of a differentially throttled vehicle is extremely difficult (the simulator allows you to try).
CG/CP is irrelevent for this vehicle, because it isn't designed to go fast enough that aerodynamics are a factor.
Four fixed position engines can give full 3 axis control if you are tricky about it. Opposite pairs of engines are canted a few degrees so that one pair of engines gives a slight positive roll, and the other pair of engines gives a slight negative roll. This does mean that there is a cross couple for every pitch or yaw adjustment, but with an order of magnitude difference between them, it is easy to correct out.
The difficulty of guidance and control is overrated.
Coming back as a glider implies wings and landing gear, which wind up massing more than vertical landing propellant.
Trying to do without wings on X-33 forced a sub-optimal tankage solution, which turned out to not work.
A VTVL isn't expected to "fly" to a landing. It plummets at terminal velocity (not as fast as you might expect, because it is mostly empty), only firing the engines a reletive few seconds before landing. The fuel required is then only a few seconds of several G thrust for the EMPTY mass of the vehicle.
A somewhat more valid argument against vertical landing is that doing it efficiently requires computer control, and it is unlikely that a human pilot would be able to do it manually without a lot more slop fuel.
It used to be that NASA had to have a string of ground stations and ships around the world to get continuous data from space vehicles. This is still an issue for countries like China, and the logistics have impacted their space program.
NASA does now use a lot of custom relay satellites, but the communications hardware is still $100k+ one-offs for each application.
Using $5k of commercial equipment that is probably better developed is indeed a good thing.
The articles also lumped together with the LEO sat communication aspect the increasing use of GPS to augment and eventually replace dedicated radar for positioning.
John Carmack
We did a ton of testing the last two weeks while we were putting the demo together.
The 733 G4 was not as fast as my 1 ghz PIII in any of the trouble areas.
Apple is doing a lot of good work, but the CPU's just aren't as fast as the x86 ones.
AltiVec can compensate in some cases, because it is way, way easier to program for than SSE, but it takes a very simple batched, computation intensive task for it to pay off in any noticable way. Amdahls law and all that.
We did a couple functions with AltiVec, but they didn't make much difference.
Video encoding and large image processing are two areas that it can pay off, because you may be spending 90%+ of your time in one page of code.
Even then, it takes a special balance to let a G4 come out ahead, because it has less memory bandwidthd than a high end x86 system.
The article lays out all the things Bill should have done:
He should have compromised what he really thought.
He should have "played the PR game".
He should have coddled bureaucrats.
He should have paid attention to "political sensibilities".
From the perspective of Fortune or Business Week, that all sounds right and proper.
But from a hacker perspective?
I'm not saying Gates is a hacker (although he is indeed really damn smart), but if you align yourself with those ideals, is it really correct to deride someone for being forthright and stubborn in the defense of their position?
I was ranting specifically about square patches that have implicit texture alignment, not curves in general. I am on record as saying that curved surfaces aren't as wonderful as the first seem, though.
It was my experience that subdivision surfaces are much more convenient for modeling free form organic surfaces, but polynomial patches can be more convenient for architectural work.
The hardware curved surfaces in upcoming hardware is basically ok, because you can have all the attributes independent of each other at each control point. My major point was that the 3DO/Saturn/NV1 botched it badly by explicitly tying the texture to the patch orientation, which prevents them from being able to do triangle like things at ALL.
Slashdot Mirror
Run the numbers.
With a 400 Isp engine, one percent of the vehicle landing mass can kill 40m/s of velocity. That is over 80 mph, which an efficient VTVL vehicle could expect to have as its terminal velocity.
A parachute masses more than 1% of its load.
There are lots of other factors that can push the decision either way, but it is certainly within the realm of feasible engineering decision.
John Carmack
Yes, this is very similar to what I am working on.
www.armadilloaerospace.com
Their current vehicle is a good deal larger than ours, has an aeroshell, and significantly, uses liquid hydrogen / liquid oxygen, a much more potent and difficult propellant than the hydrogen peroxide we use.
On the other hand, my project has been a lot faster and cheaper. I have spent about $50k and we have been working on it for nine months, versus their $400k and four years.
Our first up scale vehicle is going to be ready in a few months. It won't go very high or fast, but we can carry a person on it...
Next year, at the very least, we will have a supersonic manned rocket ship.
John Carmack
He is sort of correct.
It is easier to get a high thrust to weight ratio out of solids, even though they have a lower Isp and generally a lower total dV per stage.
To get more thrust out of a solid, you basically just need a bigger nozzle, while to get more out of a conventional liquid engine, you need a bigger nozzle, and bigger turbopumps, plumbing, and combustion chamber.
Not that I think solids on a manned vehicle are very sensible...
John Carmack
We will have a manned rocket vehicle flying by the end of the year, but it will be a modest little thing. The performance will only be about what you got out of the old Bell rocket pack, but it is fully fly-by-wire (and can be tested remotely) with active stabilization, and all the subsystems are directly scaleable to much larger vehicles.
I will probably enter as an X-Prize competitor at that point.
John Carmack
Armadillo Aerospace
I don't put a lot of stock in pinning down "firsts", even though people in general, and the media in particular, love to harp on it.
Everything is built on past work.
A lot of people like to think of creativity and innovation as something that springs from the void, but the truth is that everything is traceable to its origins.
I consider myself fortunate that I am consciously aware of the process. I can dissect all of my good ideas into their original parts, and even when there is an interesting synthesis, the transformation can usually be posed as an analogy to some previous work.
Given that fact, you will rarely find me touting anything as a "first", because I could always say it is "sort of like this thing over here, but with the principle demonstrated by this over there added to allow it to give the feature we wanted back then" and so on.
There are the occasional "eureka!" moments, but they tend to be in twitchy little technical things, not the larger ideas like "3D environment" or "multiplayer gaming".
I'm not all that concerned with our place in history. The process has been interesting enough in its own right, and lots of people have enjoyed the work as we produced it.
John Carmack
I won't get into gameplay arguments about it, but from an engine standpoint:
Pathways into Darkness was Bungie's take on Wolfenstein.
The original Marathon was Bungie's take on DOOM.
John Carmack
The FAA regs (FAR 101) used for model/high power rocketry specifically refer to "unmanned rockets", not "unpiloted rockets", so it isn't at all clear how something like this is regulated.
I have sent a query to the FAA about getting waivers for the manned rockets my team is working on, but it got booted up to Washington a couple weeks ago, and I haven't heard back yet.
John Carmack
I wind up doing my own internal PPC vs X86 benchmarks almost every year.
I'll set up whatever current game I am working on to run with the graphics stubbed out so it is strictly a CPU load. We just did this recently while putting the DOOM demo together for MacWorld Tokyo.
I'll port long-run time off line utilities.
I'll sometimes write some synthetic benchmarks.
Now understand that I LIKE Apple hardware from a systems standpoint (every time I have to open up a stupid PC case, I think about the Apple G3/G4 cases) , and I generally support Apple, but every test I have ever done has had x86 hardware outperforming PPC hardware.
Not necessarily by huge margins, but pretty conclusively.
Yes, I have used the Mr. C compiler and tried all the optimization options.
Altivec is nice and easy to program for, but in most cases it is going to be held up because the memory subsystems on PPC systems aren't as good as on the PC.
Some operations in Premier or Photoshop are definitely a lot faster on macs, and I would be very curious to see the respective implementations on PPC and X86. They damn sure won't just be the same C code compiled on both platforms, and it may just be a case of lots of hand optimized code competing against poorer implementations. I would like to see a Michael Abrash or Terje Mathison take the x86 SSE implementation head to head with the AltiVec implementation. That would make a great magazine article.
I'll be right there trumpeting it when I get a Mac that runs my tests faster than any x86 hardware, but it hasn't happened yet. This is about measurements, not tribal identity, but some people always wind up being deeply offended by it...
John Carmack
Heh. That sort of takes some of the wind out of the FSF financial conspiracy theory.
Yes, that was my blackjack winnings.
John Carmack
I should mention that really, all of this work can be traced back to slashdot.
Until a year and a half ago, I hadn't thought about space and (real) rockets since I was a kid.
I started reading slashdot for the open source coverage, but the occasional space story and the comments on them led me to the CATS prize and the other things going on in the space community.
I spent a year learning the engineering aspects and funding a few things that I considered interesting (JP Aerospace, SORAC, Space Frontier Foundation, and XCOR), and the last six months actually doing something myself.
I was sort of planning on submitting an article about the whole process at some point, but it looks like I got preempted (and our site is slashdotted)...
John Carmack
I should ammend myself, and say that the difficulty AT LOW SPEEDS is not that bad. Removing aerodynamic factors simplifies things a lot.
Doing something like hypersonic kinetic kill missile guidance still sounds, uh, non-trivial.
John Carmack
The throttle is manual, but attitude control is computer managed. The joystick input gives a target angle, and the computer deals with rates and pulses to try and get it there. Manual control of a differentially throttled vehicle is extremely difficult (the simulator allows you to try).
CG/CP is irrelevent for this vehicle, because it isn't designed to go fast enough that aerodynamics are a factor.
Four fixed position engines can give full 3 axis control if you are tricky about it. Opposite pairs of engines are canted a few degrees so that one pair of engines gives a slight positive roll, and the other pair of engines gives a slight negative roll. This does mean that there is a cross couple for every pitch or yaw adjustment, but with an order of magnitude difference between them, it is easy to correct out.
The difficulty of guidance and control is overrated.
John Carmack
I don't have an orbital timeframe. There are too many things I need to learn before I can make a credible estimate.
The timeframe I do have is:
Year 1: work out all the kinks in the VTVL demonstrator.
Year 2: manned rocket ships and ballistic flight, but still rather low altitudes.
Year 3: space (100km) shots, both unmanned and manned
John Carmack
Coming back as a glider implies wings and landing gear, which wind up massing more than vertical landing propellant.
Trying to do without wings on X-33 forced a sub-optimal tankage solution, which turned out to not work.
A VTVL isn't expected to "fly" to a landing. It plummets at terminal velocity (not as fast as you might expect, because it is mostly empty), only firing the engines a reletive few seconds before landing. The fuel required is then only a few seconds of several G thrust for the EMPTY mass of the vehicle.
A somewhat more valid argument against vertical landing is that doing it efficiently requires computer control, and it is unlikely that a human pilot would be able to do it manually without a lot more slop fuel.
John Carmack
My even-more-modest efforts are also ongoing:
www.armadilloaerospace.com
We hope to be making a properly controlled test flight within the next two weeks now that our gyros are working properly.
John Carmack
It used to be that NASA had to have a string of ground stations and ships around the world to get continuous data from space vehicles. This is still an issue for countries like China, and the logistics have impacted their space program. NASA does now use a lot of custom relay satellites, but the communications hardware is still $100k+ one-offs for each application. Using $5k of commercial equipment that is probably better developed is indeed a good thing. The articles also lumped together with the LEO sat communication aspect the increasing use of GPS to augment and eventually replace dedicated radar for positioning. John Carmack
We don't have any technology specifically directed towards character features. The animation was done pretty conventionally in Maya.
Our new animator comes from a film background, and we are finding that the skills are directly relevent in the new engine.
John Carmack
>Half Life made net profits of just over $200,000
Uh, no. Half Life made FAR more than that.
The top titles still bring in lots of money, but if you don't get a hit, you probably won't recoup your development money.
John Carmack
We moved to C++ for the current game (which does not have an official full name yet).
.plan update about it, because it has definately had its pros and cons.
I will probably do a
Jim Dose had inadvertantly used a few MS specific idioms that we had to weed out over the past couple weeks of the bring up on OS-X.
John Carmack
We did a ton of testing the last two weeks while we were putting the demo together.
The 733 G4 was not as fast as my 1 ghz PIII in any of the trouble areas.
Apple is doing a lot of good work, but the CPU's just aren't as fast as the x86 ones.
AltiVec can compensate in some cases, because it is way, way easier to program for than SSE, but it takes a very simple batched, computation intensive task for it to pay off in any noticable way. Amdahls law and all that.
We did a couple functions with AltiVec, but they didn't make much difference.
Video encoding and large image processing are two areas that it can pay off, because you may be spending 90%+ of your time in one page of code.
Even then, it takes a special balance to let a G4 come out ahead, because it has less memory bandwidthd than a high end x86 system.
John Carmack
Unfortunately, the giant projector screens are not color calibrated the same way at all.
The colors did get rather washed out on the big screen.
John Carmack
The article lays out all the things Bill should have done:
He should have compromised what he really thought.
He should have "played the PR game".
He should have coddled bureaucrats.
He should have paid attention to "political sensibilities".
From the perspective of Fortune or Business Week, that all sounds right and proper.
But from a hacker perspective?
I'm not saying Gates is a hacker (although he is indeed really damn smart), but if you align yourself with those ideals, is it really correct to deride someone for being forthright and stubborn in the defense of their position?
John Carmack
I was ranting specifically about square patches that have implicit texture alignment, not curves in general. I am on record as saying that curved surfaces aren't as wonderful as the first seem, though.
It was my experience that subdivision surfaces are much more convenient for modeling free form organic surfaces, but polynomial patches can be more convenient for architectural work.
John Carmack
The hardware curved surfaces in upcoming hardware is basically ok, because you can have all the attributes independent of each other at each control point. My major point was that the 3DO/Saturn/NV1 botched it badly by explicitly tying the texture to the patch orientation, which prevents them from being able to do triangle like things at ALL.
John Carmack
My point was that with texturing tied directly to the patch orientation, you can't do exactly the thing that you describe.
I'm not a big booster of hardware curves in any form, but I only rail against hardware schemes that use aligned textures.
John Carmack