The name of the school is still Case Western Reserve University.
Despite the fact that its OK to officially call it 'Case' now (it wasnt OK to do so in '97), CWRU is still a valid abbreviation. Plus I paid so much money to that place that I'll call it whatever I damn well please.
The comparison with shuttle IS fair, because its 60 tons to orbit is not really useful payload. True, its a life support system, but its also a crew return mechanism with features that aren't useful at all in orbit. Why count the landing gear or wings of the shuttle as payload to orbit? The new strategy is to significantly reduce the mass of the return mechanism in exchange for payload that doesnt need to be returned to earth.
The side-mount launch configuration of the shuttle IS the least safe feature of the system. Columbia is a direct result of that configuration, and its debatable if Challenger would have resulted in a loss of crew if they were being launched on an in-line system.
We already have ion propulsion that offers specific impulses 5-10 times higher than those of chemical propulsion. The problem is, the thrust magnitude is very low (= 1N) and the physics of those thrusters prevents them from operating in the atmosphere.
Now the key difference appears to be this: Ion propulsion gains efficiency by having a dramatically higher specific impulse. Some performance of ion propulsion systems is sacrificed due to its low thrust/mass ratio, but the high Isp usually more than makes up for that.
The article states "The most substantial characteristic of the technology is ten times a higher flow-out rate, which otherwise only by a nuclear fusion engine - which (still) does not exist - is attainable." This makes it sound as if they are working on the fuel efficiency problem from the other part of the equation. If this technology does infact yield a very high flow rate, its possible it has a thrust level adequate for launch vehicles. Is there any word on whether or not this technology has any limitations to being used in such an application?
In addition to a large number of contractor layoffs already occurring thoughout NASA, such as those at JPL, there will likely be a reduction in the civil-servant payroll via layoffs as well.
While I agree that we need to transition from Shuttle to something else, its not going to be a painless process. Many very skilled scientists and engineers will lose their job because it isnt applicable to the immediate needs of the human exploration program.
For a lot of space missions, needing to take up your own cumbersome wings, landing gear, and other parts for landing wastes a lot of payload capability.
Meaning that, rather than doing boring repetitive tasks manually, a good engineer usually finds shortcuts and ways to automate tasks without compromising the quality of results.
I typically don't do navigation-level detail work, but I do performance level work used to size spacecraft, determine mass/power/thrust/specific impulse levels, etc.
Generally there are two types of missions, high thrust (chemical) and low-thrust (ion engine, solar sail, etc).
For a chemical mission you need to know where and when you leave (your initial state vector), where and when you are going (your final state vector). One can solve Lambert's problem to determine the performance and trajectory. There are also software programs such as MIDAS but unfortunately I don't believe they are publicly available.
For chemical missions, you can take the delta-V result, and since the chemical system applies the delta-V nearly instantaneously, you can simply use the rocket equation to calculate your mass fraction:
delta-V = g * Isp * ln(m0/mf)
Where g is sea-level gravity, Isp is the specific impulse, m0 is your initial mass, and mf is your final mass.
What else is there to consider? Well, you want to launch at the date when the trajectory will require the least propellant, but you want a wide enough window such that if you launch a week, or two, late due to mechanical problems, your spacecraft will still have enough propellant to do the job.
Aside from programs, you can also find useful data in a 'pork chop plot,' such as this: http://marsprogram.jpl.nasa.gov/spotlight/porkchop -image01.html The pork chop plot shows contours of delta-V (in blue) vs. launch and arrival date. The red lines are lines of constant flight time. These type of plots are typicaly constructed using a tool like MIDAS or Lambert's problem, and are publically available. Here's one example http://trs.nis.nasa.gov/archive/00000438/
As someone who is interested in performance, rather than navigation, I can generally assume that the planets are massless (unless I'm doing a gravity assist). The amount that Jupiter perturbs your when youre going to Mars CAN make the difference between capturing into the correct orbit and slamming into the ground, but it has a very small affect on the amount of propellant needed.
We also often assume that the spacecraft leaves from the center of mass of Earth, and goes to the center of mass of the target body. Again, this doesnt affect performance much but the additional complexity for the optimizers usually isnt worth it.
For low-thrust missions, things are generally much more complicated mathematically. With chemical missions, you can assume instantaneous changes in velocity. But for low-thrust missions, the thrust is being applied continuously for long time durations. The number of degrees of freedom in the optimization grows substantially.
For Earth-orbiting low-thrust vehicles, simple-control laws can perform the desired maneuver (orbit raising, station keeping, etc) while minimizing propellant mass. I recommend searching NASA's techinical databases for "control laws" if youre interested.
For interplanetary low-thrust spacecraft, there are several codes used to solve the problem ranging from "performance level" accuracy to "navigation level" accuracy. One that is publically available to US citizens is OTIS. http://otis.grc.nasa.gov/ OTIS can be used to compute high-fidelity interplanetary high-thrust, low-thrust, lauhch vehicle, aircraft, and many other types of trajectories. Its very general, very powerful, but has a very steep learning curve. The developers are always looking to widen the user base, so feel free to try it out.
Is this tug going to be reusable? I mean, will it come back to low earth orbit after it drops off its payload to pick up more propellant and another satellite?
The shuttle program is already largely contracted out.
The whole "contractors do it for less money" is largely a myth. Contractors often use such programs as a cash cow.
Re:I'm all for science/technology/astronomy but...
on
Back to Moon in 2015?
·
· Score: 1
I'm completely for building a permanent research base on the mooon, but the "staging point" argument only works if you're manufacturing your spacecraft there.
Otherwise you have to launch your spacecraft components from Earth, propulsively land them on the moon, and then launch them from the Moon.
Slashdot Mirror
"written in fortran" 208,000
Didnt bother specifying Fortran4, Fortran77, Fortran90, Fortran 95
"The best way to become a millionaire in the launch vehicle business, is to start out as a billionaire."
The name of the school is still Case Western Reserve University.
Despite the fact that its OK to officially call it 'Case' now (it wasnt OK to do so in '97), CWRU is still a valid abbreviation. Plus I paid so much money to that place that I'll call it whatever I damn well please.
- '02
Next thing you know they'll buy SCO.
Yeah but fuel cells are much more efficient than combustion, so you'll get more bang for your buck.
The comparison with shuttle IS fair, because its 60 tons to orbit is not really useful payload. True, its a life support system, but its also a crew return mechanism with features that aren't useful at all in orbit. Why count the landing gear or wings of the shuttle as payload to orbit? The new strategy is to significantly reduce the mass of the return mechanism in exchange for payload that doesnt need to be returned to earth.
The side-mount launch configuration of the shuttle IS the least safe feature of the system. Columbia is a direct result of that configuration, and its debatable if Challenger would have resulted in a loss of crew if they were being launched on an in-line system.
We already have ion propulsion that offers specific impulses 5-10 times higher than those of chemical propulsion. The problem is, the thrust magnitude is very low (= 1N) and the physics of those thrusters prevents them from operating in the atmosphere.
Now the key difference appears to be this: Ion propulsion gains efficiency by having a dramatically higher specific impulse. Some performance of ion propulsion systems is sacrificed due to its low thrust/mass ratio, but the high Isp usually more than makes up for that.
The article states "The most substantial characteristic of the technology is ten times a higher flow-out rate, which otherwise only by a nuclear fusion engine - which (still) does not exist - is attainable." This makes it sound as if they are working on the fuel efficiency problem from the other part of the equation. If this technology does infact yield a very high flow rate, its possible it has a thrust level adequate for launch vehicles. Is there any word on whether or not this technology has any limitations to being used in such an application?
Generally, propellant is pretty inexpensive for launch vehicles, when compared to other systems and expenses.
In addition to a large number of contractor layoffs already occurring thoughout NASA, such as those at JPL, there will likely be a reduction in the civil-servant payroll via layoffs as well.
While I agree that we need to transition from Shuttle to something else, its not going to be a painless process. Many very skilled scientists and engineers will lose their job because it isnt applicable to the immediate needs of the human exploration program.
Which just hammers home the point...
For a lot of space missions, needing to take up your own cumbersome wings, landing gear, and other parts for landing wastes a lot of payload capability.
Actually it looks as if there may very well be layoffs at NASA in FY07.
Meaning that, rather than doing boring repetitive tasks manually, a good engineer usually finds shortcuts and ways to automate tasks without compromising the quality of results.
IAATA (I am a trajectory analyst)
p -image01.html The pork chop plot shows contours of delta-V (in blue) vs. launch and arrival date. The red lines are lines of constant flight time. These type of plots are typicaly constructed using a tool like MIDAS or Lambert's problem, and are publically available. Here's one example http://trs.nis.nasa.gov/archive/00000438/
I typically don't do navigation-level detail work, but I do performance level work used to size spacecraft, determine mass/power/thrust/specific impulse levels, etc.
Generally there are two types of missions, high thrust (chemical) and low-thrust (ion engine, solar sail, etc).
For a chemical mission you need to know where and when you leave (your initial state vector), where and when you are going (your final state vector). One can solve Lambert's problem to determine the performance and trajectory. There are also software programs such as MIDAS but unfortunately I don't believe they are publicly available.
For chemical missions, you can take the delta-V result, and since the chemical system applies the delta-V nearly instantaneously, you can simply use the rocket equation to calculate your mass fraction:
delta-V = g * Isp * ln(m0/mf)
Where g is sea-level gravity, Isp is the specific impulse, m0 is your initial mass, and mf is your final mass.
What else is there to consider? Well, you want to launch at the date when the trajectory will require the least propellant, but you want a wide enough window such that if you launch a week, or two, late due to mechanical problems, your spacecraft will still have enough propellant to do the job.
Aside from programs, you can also find useful data in a 'pork chop plot,' such as this: http://marsprogram.jpl.nasa.gov/spotlight/porkcho
As someone who is interested in performance, rather than navigation, I can generally assume that the planets are massless (unless I'm doing a gravity assist). The amount that Jupiter perturbs your when youre going to Mars CAN make the difference between capturing into the correct orbit and slamming into the ground, but it has a very small affect on the amount of propellant needed.
We also often assume that the spacecraft leaves from the center of mass of Earth, and goes to the center of mass of the target body. Again, this doesnt affect performance much but the additional complexity for the optimizers usually isnt worth it.
For low-thrust missions, things are generally much more complicated mathematically. With chemical missions, you can assume instantaneous changes in velocity. But for low-thrust missions, the thrust is being applied continuously for long time durations. The number of degrees of freedom in the optimization grows substantially.
For Earth-orbiting low-thrust vehicles, simple-control laws can perform the desired maneuver (orbit raising, station keeping, etc) while minimizing propellant mass. I recommend searching NASA's techinical databases for "control laws" if youre interested.
For interplanetary low-thrust spacecraft, there are several codes used to solve the problem ranging from "performance level" accuracy to "navigation level" accuracy. One that is publically available to US citizens is OTIS. http://otis.grc.nasa.gov/ OTIS can be used to compute high-fidelity interplanetary high-thrust, low-thrust, lauhch vehicle, aircraft, and many other types of trajectories. Its very general, very powerful, but has a very steep learning curve. The developers are always looking to widen the user base, so feel free to try it out.
Yep. The old "good thrust, who cares about Isp" mentality.
There is a reason pretty much all chemical rocket engines have throats, wonder why he fails to see it.
Its not just a matter of altitude, you need velocity. A LOT more than a jet will give you.
Looks similar to most modern heavy lift launch vehicles, except it will be designed to lift 5x more mass.
The problem is fixed by having a single-piece heat shield that wont require gap fillers in the first place.
Thats one of the reasons for a push for a capsule, the heat shield design is much simpler, better understood, and cheaper.
Is this tug going to be reusable? I mean, will it come back to low earth orbit after it drops off its payload to pick up more propellant and another satellite?
y .html
NASA has looked at similar things, though none have been built yet. http://www.grc.nasa.gov/WWW/RT2001/6000/6920verhe
"You're gonna to your doctor in about 10 years...
'Your cholesterol is out of control, what have you been doing?'
'I dont know, I've been eating right, running, doing everything right...'
'Yeah, but have you been using sunblock?'
'Well, yeah'
'Whats the matter with you!? You should know better'"
NASA doesnt make policy, it follows directives.
Our political leaders are saying to get the shuttle flying again.
The Crew Exploration Vehicle (CEV)
i cle
http://en.wikipedia.org/wiki/Crew_Exploration_Veh
The shuttle program is already largely contracted out.
The whole "contractors do it for less money" is largely a myth. Contractors often use such programs as a cash cow.
I'm completely for building a permanent research base on the mooon, but the "staging point" argument only works if you're manufacturing your spacecraft there.
Otherwise you have to launch your spacecraft components from Earth, propulsively land them on the moon, and then launch them from the Moon.
This study shows that embryonic stem cells can be derived using nuclear transfer from patients with illness
Now the nuclear boogeyman is involved.
It isnt necessary to know how something was created in order to understand how something works.
For instance, we know how gravity works, but not really what the underlying driver for it is.