Astro SG Wise
Future Orion MPCV Pilot
Regarding Newer Conceptual Design of a Manned Mars Mission
Greetings, fellow orbiters,
For the past few years, I have been contemplating the concept designs for manned Mars missions. NASA has not released much new information on their plans for Mars in 2020, which leaves me to asking as to what their design will be. The concepts I have been meditating on have been a combination of ideas from the Constellation program CTV, the current Boeing Mars designs, and NASA's game changing technologies development.
First of all, I will address my opinions, questions, and concerns on the Crew Transfer Vehicle, the stack that will bring the humans to Mars...
THE CREW TRANSFER VEHICLE
The Constellation program had a relatively-detailed artist's concept of the CTV for a Mars mission. It consisted of a bimodal nuclear thermal booster, a drop tank, and an inflatable habitat. With NASA's current budget, and if there were to be a possible dip in that budget in the future, NASA will have to come up with an affordable design. The Constellation architecture requires seven rocket launches, three of those for this vehicle. I believe that designing the stack only a little differently can save a full launch. (NOTE: The Constellation program uses the Ares V designs. Space Launch System lifts only a little less than the Ares V, and it's diameter is only a few feet less. To fit the CTV modules inside of the fairings would only require a minor shrinking in diameter.)
How do we solve the problem of an extra launch? First, we make the vehicle a hybrid. Using nuclear thermal propulsion on the Constellation CTV, the vehicle needs not only a nuclear booster, but a large drop tank of fuel. Why not make the vehicle a nuclear booster with a Solar Electric Propulsion module connected to it? Why is this a good idea? SEP thrusters can be 10x more efficient than chemical propulsion, and therefore, saving approximately 10x the fuel weight (save the fact that nuclear isn't exactly traditional chemical propulsion). While the NTR does the heavy lifting, using around half the fuel in the initial ejection burn, the SEP would cruise the rest of the way, finishing up the burn. The vehicle could be manipulated to conduct orbit insertion via the SEP. The vehicle would use the rest of the nuclear fuel for the return transfer burn, and the SEP would cruise the vehicle back to Earth.
Boeing has expressed their love of SEP in their designs. See their explaination of their Mars mission concept on video here: http://www.boeing.com/features/2014/12/bds-path-to-mars-12-04-14.page. Their stack design uses only Solar Electric Propulsion, and as one can see, this requires a large mass of ion thrusters and super huge solar panels. After hearing the reports on the efficiency vs. speed of SEP, I am not very confident that a manned mission based only on SEP is realistic. Using a NTR/SEP hybrid may be a perfect compromise.
So, how does this reduce the number of launches? The propellant tank for the SEP fuel is significantly smaller than the drop tank on the Constellation CTV for extra nuclear fuel. This is is true, such that, if one uses the full fairing capacity, and they take out any extra space in the crew/habitat module, they should be able to fit the SEP module onto the crew module. This stack would then result in two launches, one for the NTR (with the ion thrusters installed on it), and the command module, with the SEP propellant included. The two would rendezvous in orbit, and dock. If you do not understand, at this point, the Constellation program's Mars mission architecture, see this video: https://www.youtube.com/watch?v=uUBhn3_P3hU.
If you pause the video, with a good view of the space between the habitat module and the extra drop tank of the CTV, you will notice a docking access tunnel, and a ring-shaped module. There is a bunch (sort of) of unused space between this ring-shaped module and the drop tank. If you really want to fit it all perfectly in one module, get rid of that space.
Also, for SEP to work on this design, you need a lot of Solar, hence its namesake. While the cool piloted solar arrays on the Constellation stack are solar panels, they would not be enough to power the ion thrusters, and they are quite heavy with their piloting mechanisms. ATK's UltraFlex and MegaFlex solar panel technology (outlined here: https://www.youtube.com/watch?v=iqS2W0JC67w) boast ultra-light weight, compact stowage, and high power capacities. Using these, as well as the lesser-known roll out solar arrays, would allow the module to hold high-power gaining solar arrays that fit nicely and reduce weight. Of course, NASA is also quite interested in these concepts.
Also note that one NTR's worth in fuel seems a pretty small amount of fuel, compared to the NTR + droptank scenario. Actually, you get a little more fuel efficiency for the NTR in the hybrid design as well. The vehicle is now lighter than it used to be (because of SEP), and so you get more thrust for the fuel. Also, the NTR requires a propellant refrigerator, and this refrigerator does not need to be as large because it doesn't need to manage as much nuclear fuel, and thus reducing weight. The point of the weight reduction is to use less fuel and cost, while still transferring the crew to Mars in a descent time frame.
Now that we have reduced the extra space and weight, we must emphasize the power generating ability for the SEP system. The power of the ion thrust is directly associated with the amount of power. Therefore, if we want to use SEP for a manned Mars mission, we need as much power and speed as we can get. Two ultra-large circular solar panels, two large roll-out panels, solar panels integrated onto the outside surface of the NTR, and the bimodal nuclear energy generator all contribute to the SEP power. All of this, and the reduced weight, would allow the SEP to cruise successfully to Mars.
This concept has been based on the assumption that NASA's Constellation CTV stack is physically correct, and that SEP technology is enough to get the stack half way to Mars. Boeing puts all of their faith in a relatively-heavy looking SEP vehicle, and NASA has not mentioned its nuclear devices for a while, and thus accepting some practical use of SEP. I have been skeptical, for a while, of SEP. It is slow, but I would think that NASA and Boeing's trust in SEP is enough to indicate it is more than we assume. All of this is not based on any real physics, and thus, I cannot know for certain if this design works. As I post this, I hope that you will make any comments, for you may have more experience and knowledge in the studies of SEP.
Other things I have accounted for in the concept is how to fit all of this in the Space Launch System fairings, how to land on Mars, and how to get cargo down to the planet. I will address all of this later, but this image below sums up the estimated number of rockets required for the mission.
If you have any comments or things to add, I will be very grateful. Join on NASA's journey to Mars.
- Sam
Greetings, fellow orbiters,
For the past few years, I have been contemplating the concept designs for manned Mars missions. NASA has not released much new information on their plans for Mars in 2020, which leaves me to asking as to what their design will be. The concepts I have been meditating on have been a combination of ideas from the Constellation program CTV, the current Boeing Mars designs, and NASA's game changing technologies development.
First of all, I will address my opinions, questions, and concerns on the Crew Transfer Vehicle, the stack that will bring the humans to Mars...
THE CREW TRANSFER VEHICLE
The Constellation program had a relatively-detailed artist's concept of the CTV for a Mars mission. It consisted of a bimodal nuclear thermal booster, a drop tank, and an inflatable habitat. With NASA's current budget, and if there were to be a possible dip in that budget in the future, NASA will have to come up with an affordable design. The Constellation architecture requires seven rocket launches, three of those for this vehicle. I believe that designing the stack only a little differently can save a full launch. (NOTE: The Constellation program uses the Ares V designs. Space Launch System lifts only a little less than the Ares V, and it's diameter is only a few feet less. To fit the CTV modules inside of the fairings would only require a minor shrinking in diameter.)
How do we solve the problem of an extra launch? First, we make the vehicle a hybrid. Using nuclear thermal propulsion on the Constellation CTV, the vehicle needs not only a nuclear booster, but a large drop tank of fuel. Why not make the vehicle a nuclear booster with a Solar Electric Propulsion module connected to it? Why is this a good idea? SEP thrusters can be 10x more efficient than chemical propulsion, and therefore, saving approximately 10x the fuel weight (save the fact that nuclear isn't exactly traditional chemical propulsion). While the NTR does the heavy lifting, using around half the fuel in the initial ejection burn, the SEP would cruise the rest of the way, finishing up the burn. The vehicle could be manipulated to conduct orbit insertion via the SEP. The vehicle would use the rest of the nuclear fuel for the return transfer burn, and the SEP would cruise the vehicle back to Earth.
Boeing has expressed their love of SEP in their designs. See their explaination of their Mars mission concept on video here: http://www.boeing.com/features/2014/12/bds-path-to-mars-12-04-14.page. Their stack design uses only Solar Electric Propulsion, and as one can see, this requires a large mass of ion thrusters and super huge solar panels. After hearing the reports on the efficiency vs. speed of SEP, I am not very confident that a manned mission based only on SEP is realistic. Using a NTR/SEP hybrid may be a perfect compromise.
So, how does this reduce the number of launches? The propellant tank for the SEP fuel is significantly smaller than the drop tank on the Constellation CTV for extra nuclear fuel. This is is true, such that, if one uses the full fairing capacity, and they take out any extra space in the crew/habitat module, they should be able to fit the SEP module onto the crew module. This stack would then result in two launches, one for the NTR (with the ion thrusters installed on it), and the command module, with the SEP propellant included. The two would rendezvous in orbit, and dock. If you do not understand, at this point, the Constellation program's Mars mission architecture, see this video: https://www.youtube.com/watch?v=uUBhn3_P3hU.
If you pause the video, with a good view of the space between the habitat module and the extra drop tank of the CTV, you will notice a docking access tunnel, and a ring-shaped module. There is a bunch (sort of) of unused space between this ring-shaped module and the drop tank. If you really want to fit it all perfectly in one module, get rid of that space.
Also, for SEP to work on this design, you need a lot of Solar, hence its namesake. While the cool piloted solar arrays on the Constellation stack are solar panels, they would not be enough to power the ion thrusters, and they are quite heavy with their piloting mechanisms. ATK's UltraFlex and MegaFlex solar panel technology (outlined here: https://www.youtube.com/watch?v=iqS2W0JC67w) boast ultra-light weight, compact stowage, and high power capacities. Using these, as well as the lesser-known roll out solar arrays, would allow the module to hold high-power gaining solar arrays that fit nicely and reduce weight. Of course, NASA is also quite interested in these concepts.
Also note that one NTR's worth in fuel seems a pretty small amount of fuel, compared to the NTR + droptank scenario. Actually, you get a little more fuel efficiency for the NTR in the hybrid design as well. The vehicle is now lighter than it used to be (because of SEP), and so you get more thrust for the fuel. Also, the NTR requires a propellant refrigerator, and this refrigerator does not need to be as large because it doesn't need to manage as much nuclear fuel, and thus reducing weight. The point of the weight reduction is to use less fuel and cost, while still transferring the crew to Mars in a descent time frame.
Now that we have reduced the extra space and weight, we must emphasize the power generating ability for the SEP system. The power of the ion thrust is directly associated with the amount of power. Therefore, if we want to use SEP for a manned Mars mission, we need as much power and speed as we can get. Two ultra-large circular solar panels, two large roll-out panels, solar panels integrated onto the outside surface of the NTR, and the bimodal nuclear energy generator all contribute to the SEP power. All of this, and the reduced weight, would allow the SEP to cruise successfully to Mars.
This concept has been based on the assumption that NASA's Constellation CTV stack is physically correct, and that SEP technology is enough to get the stack half way to Mars. Boeing puts all of their faith in a relatively-heavy looking SEP vehicle, and NASA has not mentioned its nuclear devices for a while, and thus accepting some practical use of SEP. I have been skeptical, for a while, of SEP. It is slow, but I would think that NASA and Boeing's trust in SEP is enough to indicate it is more than we assume. All of this is not based on any real physics, and thus, I cannot know for certain if this design works. As I post this, I hope that you will make any comments, for you may have more experience and knowledge in the studies of SEP.
Other things I have accounted for in the concept is how to fit all of this in the Space Launch System fairings, how to land on Mars, and how to get cargo down to the planet. I will address all of this later, but this image below sums up the estimated number of rockets required for the mission.
If you have any comments or things to add, I will be very grateful. Join on NASA's journey to Mars.
- Sam
