X-37B launch with light sail succefully launches

[dragon]

Rocket with X-37B space plane, LightSail craft successfully launches

By Jamie Lendino on May 20, 2015 at 2:10 pm12 Comments

X-37B launch
Share This article
37

The United States Air Force’s X-37B space plane and the Planetary Society’s LightSail spacecraft both launched today aboard a United Launch Alliance Atlas V rocket. The launch took place at 11:05am EDT from Florida’s Cape Canaveral Air Force Station. As we reported yesterday, details about the X-37B’s highly classified mission are hard to come by, although we do know that part of the mission is to test a new Hall thruster, an electric propulsion device that ionizes and accelerates a gas such as Xenon in order to increase fuel economy and payload capacity, if not outright thrust.

You can watch a replay of the OTV-4 mission takeoff and the first few minutes of the rocket’s launch above the Earth’s surface below.

The X-37B will also carry aboard a NASA payload called the Materials Exposure and Technology Innovation in Space (METIS) investigation, which will help researchers figure out how being in space affects over 100 different kinds of materials. “By exposing materials to space and returning the samples to Earth, we gain valuable data about how the materials hold up in the environment in which they will have to operate,” said Miria Finckenor, the co-investigator on the MISSE experiment and principal investigator for METIS at NASA’s Marshall Space Flight Center in Huntsville, Alabama, in a statement. “Spacecraft designers can use this information to choose the best material for specific applications, such as thermal protection or antennas or any other space hardware.”

Investigations like this have helped engineers decide on materials for missions like the Mars Curiosity rover, the James Webb Space Telescope, and SpaceX’s Dragon spacecraft. Beyond that and the Hall thruster test, the rest of X-37B’s mission remains a mystery. wierd thats it's technically a classified mission using a semi secret military spacecraft

Solar sail LightSail

We know a lot more about the LightSail (pictured above). Originally conceived by the famous late astronomer Carl Sagan, the LightSail employs its namesake for propulsion, and will now be tested in the Earth’s upper atmosphere to ensure the sails deploy correctly. Solar sail technology works because light has just a little bit momentum that you can transfer to a spacecraft — enough to guide it and push it along. The LightSail is a tiny craft with 32 square meters of mylar material, as well as a comm system, solar panels, a computer, batteries, and some other flight-related parts.

If the current test goes well, the Planetary Society plans to begin preparation for a real mission in April 2016 in low Earth orbit. As for the X-37B, aside from the NASA experiments, we’ll just have to wait for whatever the military deems we’re allowed to know.

link

[Balrog]

Nifty.

Since we won't hear about the cool pew pew lazer guns the X-37B is flying around with for another few years, how would solar sails compare to other methods of propulsion as a practical method of intra-system travel?

[Borgholio]

Nifty.

Since we won't hear about the cool pew pew lazer guns the X-37B is flying around with for another few years, how would solar sails compare to other methods of propulsion as a practical method of intra-system travel?

Quite practical actually, at least if you're heading out. I'm not sure how well it will work if you're heading from the outer solar system to the inner system, since I don't believe the sailboat method of tacking against the wind would work with a solar sail...

[Imperial528]

Actually, it kind of does. Here, I'll make a diagram with text:

-> Ship's velocity vector.
=\ Ship
^ Solar wind

This is a prograde "burn"

->
=\
^

This is a retrograde "burn"

->
/=
^

[SpottedKitty]

Since we won't hear about the cool pew pew lazer guns the X-37B is flying around with for another few years, how would solar sails compare to other methods of propulsion as a practical method of intra-system travel?

Look up Arthur C. Clarke's short story Sunjammer. Written fifty years ago, but it's still a valid look at how a solar sail would work.

[Sky Captain]

Problem is it would take nearly forever to get anywhere with light sail if using only natural sunlight because thrust is so low. A mission with human crew that uses lightsail propulsion would require some sort of monster laser to illuminate the sail and provide some useful thrust

[SpottedKitty]

Problem is it would take nearly forever to get anywhere with light sail if using only natural sunlight because thrust is so low.

Very true, except for one thing — the thrust does not stop. It's similar to the situation with ion engines, the thrust is just a matter of ounces, but it can be kept running for days, or weeks, or months as long as the reaction mass holds out. And a sail has the added advantage of not needing any fuel; that tiny thrust of a few ounces just keeps piling up and up until the next thing you know, you've run up a pretty good delta-v and you're halfway to Mars orbit.

[orbitingpluto]

Problem is it would take nearly forever to get anywhere with light sail if using only natural sunlight because thrust is so low. A mission with human crew that uses lightsail propulsion would require some sort of monster laser to illuminate the sail and provide some useful thrust

Lightsails are not suited for humans- just like kites aren't. Time will tell how well they work in practice, but at the moment they promise propulsion with zero need for propellent, so a lightsail powered spacecraft can be built much lighter than a chemical or electric powered spacecraft. That alone would enable missions to host of different targets at cheaper costs, since it cold ride a smaller rocket to LEO, or deploy as a rideshare on a comsat launch.

[Borgholio]

Lightsails are not suited for humans- just like kites aren't.

Humans have been using kites for propulsion for thousands of years. Sailboats work quite well to transport humans.

[orbitingpluto]

Lightsails are not suited for humans- just like kites aren't.

Humans have been using kites for propulsion for thousands of years. Sailboats work quite well to transport humans.

I didn't think that thought out properly before typing it. If I did, I might have chose to explain my point rather than going for what is, in hindsight, a poor analogy.

Now that I'm thinking about it, I'm wondering if my belief that lightsails are less than useful for moving humans about is based on anything firm- I'll have to do some reading.

[Guardsman Bass]

Not an engineer, but I had an idea for a light-sail ship to carry people to Mars based off of a similar idea for using solar-electric propulsion. You launch into orbit, then have it slowly (as in over weeks or more) spiral outwards, picking up speed as it tacks against the solar wind. You could even put it on an elliptical orbit to use gravitational assists to go even faster. Then at some point, you launch up your human crew on a conventional chemical rocket and have it rendezvous with the Solar Sailer, before it spirals outward too far.

Repeat same process when you're at Mars, except maybe using the gravitational assists to slow you down instead. In fact, the spiral inward would be good because you could still likely control rovers on the planet's surface in real-time while that happened.

[Borgholio]

Now that I'm thinking about it, I'm wondering if my belief that lightsails are less than useful for moving humans about is based on anything firm- I'll have to do some reading.

Well (and I'm just making these numbers up as an example), if a lightsail takes a year to get people to Mars but a traditional rocket can do it in 6 months...then the rocket would be the best choice. The limiting factor on manned exploration is food and the endurance of the human body. For unmanned probes or resupply missions, a lightsail would be great because it is much cheaper and more renewable than a rocket, and the extra time doesn't matter quite as much.

For long-range exploration beyond Mars, then a lightsail or ion drive would be ideal since at those distances they would easily have the time to reach a greater speed than any chemical rocket could. Now like I said, I'm just making up numbers as example...but the general idea in either case is that if a lightsail can get humans to their destination nearly as a fast or faster than a chemical rocket, it would be a good idea to consider using one.

Or...and I just thought of this as I was about to hit "Submit"...use a chemical rocket to give the initial boost then deploy a sail to give a little bit extra speed and shorten the trip that much more.

[Guardsman Bass]

With Mars, it's hard to beat just using regular rockets and a convenient launch time. There's nothing else out there that could get you to Mars faster than the six months trip by chemical rockets that isn't totally speculative at this point.

I agree they're great for long-range unmanned missions, though. You could send probes to the outer solar system and elsewhere with much more stored propellant for use once they get there.

[loomer]

They might also have some use in supplementing more traditional mechanisms for manned missions. Every little bit of free thrust you can get for a mission to the outer solar system, or for braking when travelling inwards, is a little more propellant you don't need. If the weight trade-off of the sail versus the propellant is in favour of the sail for the total amount of DV gained during the course of a flight then supplementary sails have a place - and might also have some additional utility in helping provide shade for the main body of a craft, which seems like an odd notion but could be quite helpful when dealing with heat-intensive vessels with cooling-limited options. The less light that casts on your craft, the less heat it can impart, and savings of just a few watts here and there can add up.

[jwl]

I've been thinking: if you are doing a light sail mission to Jupiter, would it be better to aim towards the sun or away from the sun at first? Going away from the sun would reduce distance and take away the need for "tacking"; but going towards the sun would give you a greater amount of radiation, which would allow you to build up more momentum.

[SpottedKitty]

I've been thinking: if you are doing a light sail mission to Jupiter, would it be better to aim towards the sun or away from the sun at first?

A lot depends on the precise orbital geometry — where the planets are in their orbits at the time you want to travel. It's related to the reason why there are launch windows for interplanetary trips, e.g. the Mars window is open for a few weeks about every two years. Outside that time, the energy needed goes up because the planet you're aiming for isn't quite going to be in the same place as your spaceship. Setting up a daisy chain of gravity slingshots can help a lot if you aren't in a hurry (look at how long it's taken some recent missions to reach their targets). Sometimes it will make sense to head outwards first, sometimes it'll be inwards.

Incidentally, this is why some kind of constant-thrust drive is such a big thing in SF. Conventional chemical rockets give your ship a swift kick in the superstructure on launch, then it just drifts. When you reach your destination, rockets can be used again, or if there's an atmosphere, you can aerobrake against it. Try not to lithobrake, it gets messy. This limits your options for when you'll be able to launch. If you're thrusting all the way, you can launch at almost any time and the trip will usually be a lot shorter.

[orbitingpluto]

The orbit of the X-37B has been figured out by skywatchers, link to the article here.

Observers this week spotted the craft flying overhead in a 194 by 202 mile orbit (312 X 325 km), tilted 38 degrees relative to the equator.

That perch is lower than previous X-37B missions and the inclination is lower, too.

“OTV 4 entered the lowest initial altitude of the program,” said Ted Molczan, a respected satellite observing hobbyist.

“The ground track nearly repeats every 2 days. Frequently repeating ground tracks have been a common feature of the program. This could be an indication of a surveillance mission, or it may offer some operational advantage I have yet to figure out.”

With an inclination that low, this X-37B doesn't pass over Russia or the Ukraine. Just something I figured out looking over a map.

[SpottedKitty]

A two-day repeat and very low orbit certainly sounds like some kind of surveillance mission. A technology testbed, maybe? IIRC that's what the X-37B was intended for.

Come to think of it, that is a very low orbit; anyone know if previous missions have shown much orbital maneuvering capability so it can boost higher? If it stays that low, it won't stay up long.

[salm]

Is there something keeping a lightsail from scaling up? I mean, if your lightsail to mars is too slow why not just make one ten times larger?

Or prehaps lightsails would make a good addition to a conventional rocket? Sort of like a space Prius.

[Borgholio]

Is there something keeping a lightsail from scaling up? I mean, if your lightsail to mars is too slow why not just make one ten times larger?

Material strength mainly. Materials thin enough to be made into sails would not be able to withstand the stress of being too big.

Or prehaps lightsails would make a good addition to a conventional rocket? Sort of like a space Prius.

Yeah they would be a great addition. Boost up to speed with a chemical rocket, then deploy the sail for additional continuous thrust. Also can use it to slow down once you reach your destination.

[salm]

Material strength mainly. Materials thin enough to be made into sails would not be able to withstand the stress of being too big.

Is that such a problem in space? I mean there are no significant forces like gravity or wind or things like that.

And if there are whatever kinds of forces could one not simply use several sails the size of Bill Nyes sail and then stick them together with robust connectors.

[Borgholio]

Well even in space you can have forces pulling and twisting on the sail. If you want to change direction you will have to adjust the orientation of the sail. Done too quickly then it can rip or collapse. Then of course there's the whole problem of making it sturdy enough to get into orbit and withstand deployment in the first place...

[SpottedKitty]

Is that such a problem in space? I mean there are no significant forces like gravity or wind or things like that.

You're forgetting something — the force of sunlight that the sail's intended to use to accelerate the spacecraft. All of that force is concentrated on the sail fabric and whatever connections there are between the sail and its supporting structure. That's the "significant force" the sail must be built to withstand. Just because something's in space only simplifies the forces acting on it when it accelerates, the forces don't magically vanish.

[orbitingpluto]

Wikipedia has a section on the first X-37B mission about it's observed orbits, and has been seen to change it's orbit from time to time, though Wikipedia doesn't have similarly useful sections for the other two X-37B missions. The X-37Bs engine(the AR2-3) was the rocket engine used with the NF-104, which is neat.


On light sails, I found slides from a presentation with some info on how some recent light sail designs(Warning: 32mb PDF file). I'm still drawing conclusions, but I thought I'd share this.

[salm]

So would it be possible to link several sails together with more sturdy connectors? Or would the required mass of the connectors eat up the advantage of the sail being larger? Is there, so to say, a known optimal size of a sail?