Solar super-sail could reach Mars in a month

Aye-aye, sir!

I was thinking, the article says,

“A rocket would take the craft to low-Earth orbit, 300 kilometres up. After the craft unfurls a solar sail 100 metres across, a transmitter on Earth would fire microwaves at it to heat it up. The Benfords calculate a one-hour burst of microwaves could accelerate the craft to 60 kilometres per second, faster than any interplanetary spacecraft to date.”

Then I did a little math.
60,000 meters per second divided by 3600 seconds in an hour gives an acceleration of 16.7 meters per second squared. That is 1.7 gees. You could launch from the ground if the atmosphere were not a problem. If the sail could be unfurled quickly enough, then a suborbital rocket could send it to 300 kilometers where the 1.7 gee beam power should have no problem to propel it to escape velocity. And 300 km suborbital flights are much cheaper than LEO flights.

(EDIT) And by the way, what is the current status of propelling vehicles from the ground with laser light, like this?
http://www.space.com/businesstechnology ... 00705.html

Not very far along at all. The big problem is that you need a really REALLY *REALLY* powerful laser, with an insanely accurate aiming system (if you miss, the poor sucker's stranded with no propulsion whatsoever).

Also, how the devil would the thing slow down? There's no beam near Mars to catch it, unless you're assuming that it'll be caught by Mars' gravity well -- in order to do that, it'd have to essentially slam into the planet at full speed. Of course, they might be thinking of aerobraking.... But either way, the sail itself gets destroyed.

I still like fission/fusion rockets better. One piece, all reuseable, really powerful (and really fast).

[EDIT] Think "Mars in 4 hours *FLAT* kinda fast. [/EDIT]

You might want to check my math, but wouldn't that require about 110 G acceleration for 2 hours and 110 G deceleration for the other 2 hours?

The concept requires a beam of 60 megawatt - if the equipment required would be built it would be interesting for other purposes too. So it would be a very interesting multi-purpose technology.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

Hrm....... Mars is 110 million miles away (roughly, at closest approach), which translates to about 242,000,000km. Therefore, using the equation for motion from standstill [dX=a*(dt)^2], we plug in (242000000)/2=9.8*(dt^2) => 121000000/9.8=dt^2 => ~12346938.78=dt^2 => ~3513.82=dt. Note that dt is in seconds. Thus, we divide dt by 3600 (the number of seconds in an hour), to find dt=~0.976hr. This is the time for half the trip. The second half will take exactly the same time (dt does not depend on which direction you are accelerating, just the rate at which your are accelerating), giving us a total trip time at closest approach of ~2 hours.

Note that for a vehicle of any size, this would require a engine with a huge specific impulse, or just a *LOT* of fuel. It can very definitely be done though.

Please check my math and see if I'm wrong.

You made several errors.

Mars’ closest approach is about 35 million miles. That should make it faster though.

At 1.6 kilometers per mile, 110 million miles would be 176,000,000 km, not 242,000,000.

If “dX” is in kilometers then “a” needs to be in kilometers per second squared. You have used 9.8 meters per second squared instead of 0.0098 km/sec.^2.

So my result is:
Mars is 35,000,000 miles away or 56,000,000 kilometers. Half that is 28,000,000 kilometers or 28,000,000,000 meters.
28,000,000,000 = ½ * 9.8 * t^2
75,593 = t
About 21 hours.
So at 1G the total 35 million mile trip is 42 hours. Still pretty fast.

Wow. I did screw that one up. Then again, I did it off the top of my head (which is always a bad thing) and I was worrying about a physics test I just took a couple hours ago (which is always an even worse thing). Besides that, I couldn't find the notes I made on the equation. I'm really not sure where the 2.2 came from..... And an acceleration of 9.8 kilometers per second squared... <SLAP!>

Anyways, forget 4 hours, but 42 is definitely saleable....

In between boosting vehicles the beam could be pointed at Mars. If it was defocused a little you could keep the landing site warm...

Ummm.... Much to the chagrin of anybody who happens to be standing there at the time.........