Amplified photon thruster could shorten the trip to Mars from 6 months to a week

http://www.photonics.com/content/news/2007/September/7/88894.aspx

"TUSTIN, Calif., Sept. 7, 2007 -- An amplified photon thruster that could potentially shorten the trip to Mars from six months to a week has reportedly attracted the attention of aerospace agencies and contractors...."

(image hosted by imgred.com)

COOL! I'm having a very hard time understanding exactly what it does. The other scary thing is that it only made 35uN of thrust from 'off the shelf components.' I wonder what kind of power it took to make that thrust? Propulsion is nice, but if it isn't efficient, it isn't useful. The satellite aspect is intriguing though. Satellites that don't have an effective life 'limit' because of fuel running out.

When I was a kid, my fave book was a fictional "operator's manual" for a would-be spacecraft to make the Earth-Mars loop. I believe the book said it would be an 18-month journey to Mars and 24 months back. 18 months of Mars mission would make it a five-year mission "where no one has gone before" hahaha. So, I love to read about these new propulsion technologies.

This particular article was a press release written for the Bae Institute, it is not a journalism piece. SO... take with a grain of salt.

...Um... a week to MARS?

Has anyone done the math on the G-force the crew would be subjected to, to travel that distance in that amount of time?

Not that it's going to happen in my lifetime.

I don't know enough calculus to work it out....

The article is quite vague about the details of how the thruster works. That aside, I personally believe that Mars will be effectively out of the reach of mankind if it will always take months to reach it. Offering little more than cold rocks and thin air, Mars is not enough draw to justify the time, money and risk to go there, let alone colonize it.

When I was a child, I had one of those children's science books.

One article described the concept of the "ion electric rocket".

The first two captions read as follows:

An ordinary flashlight gives an immesurably slight kick when it is turned on.
The electron gun in a television set gives a bigger kick, although still far too small to be measured.

You get the drift. Must have been a child flashoholic to memorize that.

havand said:

COOL! I'm having a very hard time understanding exactly what it does. The other scary thing is that it only made 35uN of thrust from 'off the shelf components.' I wonder what kind of power it took to make that thrust? Propulsion is nice, but if it isn't efficient, it isn't useful. The satellite aspect is intriguing though. Satellites that don't have an effective life 'limit' because of fuel running out.

Click to expand...

I too am interested in it's efficiency.

The main downside is that the efficiency (not power input) is achieved by bouncing the beam many, many times between the laser bearing spacecraft (or base station) and mirrors many many times allowing the photons in the laser to be "reused" over and over for momentum transfer.

This will be AWSOME for ultra precise station keeping for interferometry observatory satellite formations, probably allowing for the eventual resolving of earth-like/earth sized worlds around other stars.

While technically possible, using this to drive a probe within a week to Mars is a much more daunting task engineering wise. Although there would be no problem with the G-forces on the crew. The thrust from such a photon drive would be miniscule. The crew would be unable to detect the acceleration with thier bodies, and it would seem indistinguishable from microgravity.

However, the miniscule thrust would be constant, and would build up over time, every second of every minute, every minute of every day for the duration of the mission, at least until they reached "turnaround" and would need to start breaking for insertion into Mars orbit. Think of it this way, what if you had a car that could only accellerate (and brake) at one mile per hour, per hour? That would suck. But what if you had to go a million miles? On that trip I'd much rather have that car than one that could go from 0-60 in 3 seconds, but only had a maximum speed of 200mph.

Besides consumables, food, water oxygen, or the weight penalties of closed-loop recycling sytems and gardens etc. the main advantage of rapid transit times is radiation. The shorter the trip, the shorter the time the crew is exposed to solar radiation, the possibility of solar flares, and cosmic ray activity. You can configure the ship in interesting ways to add shielding by using propellant tanks, water tanks, or moon rock for shielding, but all also have considerable weight (more appropriately mass) penalties, and if consumable tanks are used as double duty radiation barriers, the protection factor obviously decreases as the consumables are, well consumed.

goldenlight said:

...Um... a week to MARS?

Has anyone done the math on the G-force the crew would be subjected to, to travel that distance in that amount of time?

Not that it's going to happen in my lifetime.

I don't know enough calculus to work it out....

Click to expand...

You don't need calculus

d=1/2(a)(t^2)
t=sqrt(2d/a)

Figure a 100 million km ballistic arc at close to perigee, and 10m/s^2 for acceleration. You want to calculate the time for 1/2 the distance since you're going to be accelerating 1/2 the time, and decelerating the other 1/2 the trip. That gives you 50'000'000'000m for the target distance.

t=2*(sqrt((2*5e10m)/(10m/s^2))=2*sqrt(1e10s^2)=2*100'000s =

~ AROUND 55 HOURS ! if you can manage to accelerate at 1G the entire time

Since a week is about 168 hours, then I assume that they are aiming for around 0.5g acceleration the entire time.

For a craft with a mass of 100 metric tons, that would require an initial impulse of 50'000 [Correction: 500'000] Newtons.

Sounds nice, but a portable photon source with the capability to generate 50,000 nt (or about 12,000 lbs) of backthrust would make a HECK of a weapon. In fact a photon source with 1 lb of backthrust would make a heck of a weapon.

Sounds nice, but I have my doubts.

What are being "thrust out" are photons, so essentially this is a glorified laser being used as an engine. The force comes from the light pressure against the rear reflector of the laser's optical cavity.

meuge said:

You don't need calculus

Click to expand...

Hey Meuge, don't forget about decelerating the craft to enter orbit. Sounds like a bumpy ride hahaha...

scott.cr said:

Hey Meuge, don't forget about decelerating the craft to enter orbit. Sounds like a bumpy ride hahaha...

Click to expand...

I did account for that, by ensuring that 1/2 the trip is dedicated to deceleration.

I was assuming a 0 m/s relative velocity when the craft launches... which you could assume is = orbital velocity. Thus, when the craft arrives, it will be at the same velocity.

But overall, for a craft that's capable of sustained 1G thrust, orbital maneuvering is almost irrelevant.

P.S. Some more calculations:

For a craft using a mass driver (ion drive) as a propulsion system, if we assume a 10:1 fuel to payload ratio, with thrust sustained for 100 hours (let's assume the ship has spare fuel), the ship would have to be capable of accelerating 25-250g of reaction mass to 4.1e7 m/s... or ~41'000km/s or 13% of the speed of light... in order to impart a 1g acceleration to the craft.

This is actually theoretically quite possible, but practically the engineering required is far off, and until we develop controlled fusion reactors, nothing could provide the amount of energy necessary to drive this ship.

We can calculate the latter by calculating the initial (greatest) power requirement. 500'000N acting over the first meter at 10m/s is 5'000'000J/s. Even assuming an 80% efficiency is delivering generated power, that would mean that the ship's power plant would be required to generate >6 Megawatts.

The requirements for a photon-powered ship would be FAR greater, since the loss factor would be more like 1:10 or even higher, requiring probably close to 100 Megawatts to be generated on board the ship... which would still have to weigh only 100 tons.

Also, keep in mind they've drivven the efficiency of this photon drive by capturing the beam and getting 10-20 thousand "bounces" out of it between sets of mirrors.

So for an effective spacecraft to function 1/2 of the mirrors have to "stay home". So it's really just a new spin on the launch-laser and light sail, however no matter how good the collimation of the beam is, you're going to run up against the Raliegh length of any given frequency used and the size of the emitter surface.

The mirrors at home, and on the spacecraft and the support structures that would allow for the photons to be "reused" so many times would start being the size of the worlds themselves. Assuming there's also a laser station or mirrors on Mars to decelerate the spacecraft, so you only need to maintain optimal focus for 1/2 the trip. (And ignoring orbital seperation and the sun getting in the way once a year...) you're looking at some very impressive optics.

This will probably be good for maintaining very precise formation flying for satellite constellations, but it probably won't be very practical for long-distance travel.

Whatever drive technology is used, I'll have to hand it to the first people who step into a rocket and head off to Mars -- I wouldn't have the guts to do it.

This may not happen in my lifetime but I think it will happen. Maybe not this way but I believe man will be on Mars within a 100 years or sooner. Travel back in time 100 years to 1907 and ask people what they think about putting someone on the Moon? I be they would all laugh. We'll we put someone on the moon in what, 1969. Someday, it will happen.

Do you believe in science fiction? I got a 900+ lumen light (like most of you) and it doesnt produce a noticeable recoil (of course it doesnt). Maybe a light source that consumes the whole output of a power plant could produce some thrust. Have you ever seen a flying power plant?