NASA Test Fires New RS-25 Engine

[Hobbes]

I appreciate it, Rod Snell and Dave70968. Truly, for many years I have wondered about this. Honestly, if ya'll had not explained it in this way, I would not have seen the thrust in this light.

So, this leads to another question I have pondered: would not the moon be a good place to launch from? I mean, with the weak gravity, escape velocity could be increased significantly. This trip to Mars that will take, what, around a year? Well, if launched from the moon, might it not take a matter of days?

I believe there are some preliminary concepts to establish a base on the moon and use that as a jump point to Mars and beyond.
The moon actually provides some materials that could be used for construction and fuel, but that is a long distance goal.

A moon base also makes a good scientific outpost.
No atmosphere to obscure telescope images.
The far side would shield radio telescopes from earth radio signals.

^^^ Nice pic BTW

 

[Dave70968]

I appreciate it, Rod Snell and Dave70968. Truly, for many years I have wondered about this. Honestly, if ya'll had not explained it in this way, I would not have seen the thrust in this light.

So, this leads to another question I have pondered: would not the moon be a good place to launch from? I mean, with the weak gravity, escape velocity could be increased significantly. This trip to Mars that will take, what, around a year? Well, if launched from the moon, might it not take a matter of days?

"Escape velocity" probably isn't the term you meant to use. Escape velocity is speed necessary to get away from a body's gravity. For Earth, escape velocity is 11.2 km/sec; for the moon, it's 2.4 km/sec. Thus, to escape Earth's gravity, you'd be going more than four times as fast as you'd need to go to escape the moon.

So, would a lunar launch pad be efficacious for a quad set of RS-25s?

Actually, probably not. Rocket engines (specifically, the nozzles) are designed for maximum efficiency at a given air pressure; first-stage engines are going to be optimized for use at or near ground level, while higher-stage engines will be profiled to be more efficient in a vacuum. Engines for use on the moon would always be operated in a vacuum, so they'd be designed with that in mind.

 

[Rod Snell]

This trip to Mars that will take, what, around a year? Well, if launched from the moon, might it not take a matter of days?

The 500 # gorilla in going to Mars is the Sun's gravity, and getting to Mars in a matter of days would require more fuel and energy than anything we can now make. The path to Mars is a long gentle spiral between earth orbit and where mars will be at arrival time. Sort of like going up a winding road to get to the top of a mountain instead of trying to drive straight up a cliff.
The most efficient launch in theory would be in an orbit about halfway out to luna in a plane that would already have a lot of momentum in the right direction. Sort of like launching east from Canaveral for earth orbit to take advantage of the 1000 mph earth rotation speed.
So why don't we do that? Well, see any suitable space stations out there to fuel and service a space ship? Nope.

Orbital mechanics is a strange science where you learn that if you increase speed, you go up, and a straight line out of a gravity well requires incredible power.

 

[dennishoddy]

Good thread. Learned a lot from it.

 

[Hobbes]

The 500 # gorilla in going to Mars is the Sun's gravity, and getting to Mars in a matter of days would require more fuel and energy than anything we can now make. The path to Mars is a long gentle spiral between earth orbit and where mars will be at arrival time. Sort of like going up a winding road to get to the top of a mountain instead of trying to drive straight up a cliff.
The most efficient launch in theory would be in an orbit about halfway out to luna in a plane that would already have a lot of momentum in the right direction. Sort of like launching east from Canaveral for earth orbit to take advantage of the 1000 mph earth rotation speed.
So why don't we do that? Well, see any suitable space stations out there to fuel and service a space ship? Nope.

Orbital mechanics is a strange science where you learn that if you increase speed, you go up, and a straight line out of a gravity well requires incredible power.

It's elegant, isn't it?

 

[Junior Bonner]

"Escape velocity" probably isn't the term you meant to use. Escape velocity is speed necessary to get away from a body's gravity. For Earth, escape velocity is 11.2 km/sec; for the moon, it's 2.4 km/sec. Thus, to escape Earth's gravity, you'd be going more than four times as fast as you'd need to go to escape the moon.



Actually, probably not. Rocket engines (specifically, the nozzles) are designed for maximum efficiency at a given air pressure; first-stage engines are going to be optimized for use at or near ground level, while higher-stage engines will be profiled to be more efficient in a vacuum. Engines for use on the moon would always be operated in a vacuum, so they'd be designed with that in mind.

Well, there is merit in what you are saying. And I was merely speculating that the speed of leaving from the moon would be exceedingly fast if we used these RS-25s. That initial ignition of rocket fuel that we use on earth - I guess it would be catastrophic in a vacuum? Now, I don't know these things. It just seems like the moon could be used as a launch platform.

 

[farmerbyron]

I appreciate it, Rod Snell and Dave70968. Truly, for many years I have wondered about this. Honestly, if ya'll had not explained it in this way, I would not have seen the thrust in this light.

So, this leads to another question I have pondered: would not the moon be a good place to launch from? I mean, with the weak gravity, escape velocity could be increased significantly. This trip to Mars that will take, what, around a year? Well, if launched from the moon, might it not take a matter of days?

Mars is a really, really long ways away. Even at its closest point.

http://www.distancetomars.com


It takes light 4 minutes to travel one way when it's at its closest point and approximately 20 minutes when it's on the other side of the sun. For the trip to take hours, the speed required would be astronomical and as to this point unattainable. Not to mention the amount of energy required to slow down at the destination is prohibitive as well. Remember the voyager encounter with Pluto was a drive by because the energy required to slow it down was impossible to attain.

 

[Perplexed]

Not me. Maybe Kirsten Joy Weiss, but not me.

This is OT, but I had to google the lady in question. Probably not a good example of firearms safety, but dang...

 

[Junior Bonner]

Mars is a really, really long ways away. Even at its closest point.

http://www.distancetomars.com


It takes light 4 minutes to travel one way when it's at its closest point and approximately 20 minutes when it's on the other side of the sun. For the trip to take hours, the speed required would be astronomical and as to this point unattainable. Not to mention the amount of energy required to slow down at the destination is prohibitive as well. Remember the voyager encounter with Pluto was a drive by because the energy required to slow it down was impossible to attain.

Well, I'm like a Pre-K'er when it comes to these academic questions. But with very little gravity on the moon, a quad set of RS-25s could lift off with less friction.

And once mars was in sight, the vessel could use thrusters to swing it about and slow it down. The tremendous power inherent with the RS-25 platform would create a mass with which the host entity could apply a force resulting in an equal and opposite reaction.

 

[Dave70968]

Junior, if you're interested in learning more about the basics of orbital mechanics, you could do a whole lot worse than to play Kerbal Space Program. The demo version is available for free at their website: https://kerbalspaceprogram.com/en/