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Gullible Jones
2014-Mar-24, 02:17 AM
I did some cursory reading on these and thought they looked interesting, so of course I have some questions.

1. Would it be possible, or plausible, to create a yacht-style solar sail that would accelerate towards a radiation source? How about for electric sails?

2. What do existing designs for electric sails (i.e. using the solar wind) look like, in physical terms? How physically large would they have to be when fully unfurled, in order to be useful?

3. Could any sort of sail whatsoever be practical for human missions, or are we talking about excessively large dimensions here?

4. How does radiation pressure from solar wind compare to solar light in terms of Newtons?

5. For those in the know: what sort of budget, at a minimum, might go into developing a workable space probe based on an electric sail?

Noclevername
2014-Mar-24, 02:35 AM
1. No, though IIRC "tacking" is an option for certain circumstances.

2. Wires sticking out straight. A Magnetic sail would use a large (miles wide) ring of superconductors.

3. Yes and yes. Square miles, tens to hundreds.

4. It's less, that's all I know.

5. It's already been done: http://en.wikipedia.org/wiki/ESTCube-1

cjameshuff
2014-Mar-24, 04:14 AM
Photon pressure gives about a thousand times as much thrust as the solar wind for a given cross section. And electric sails can only produce outward thrust, though magsails can tack to some degree.

Noclevername
2014-Mar-24, 05:19 AM
And electric sails can only produce outward thrust, though magsails can tack to some degree.

Magsails also have the advantage of being able to thrust against a planet or moon's magnetosphere.

ravens_cry
2014-Mar-25, 01:15 AM
I can see such being useful for unmanned cargo vehicles carrying storable items on regular flights. It doesn't matter how long it takes to get to the destination as long as the time between flights is short enough once the initial flight is over.

Noclevername
2014-Mar-25, 01:42 AM
Magsails do have one advantage; as they move into the outer solar system, away from the Sun, their own magnetic field can expand to catch more solar wind particles and maintain a fairly even thrust, even at distances where the Sun is just a fairly bright star and a lightsail would be unable to even twitch.

Ilya
2014-Mar-25, 05:51 PM
I did some cursory reading on these and thought they looked interesting, so of course I have some questions.

1. Would it be possible, or plausible, to create a yacht-style solar sail that would accelerate towards a radiation source?
If you start out in orbit around the Sun -- which of course all space probes do, -- it is possible to angle the sail so that the direction of thrust is opposite to the probe's orbital velocity (and approximately perpendicular to the Sun-probe line). That will act as a brake on the probe and cause it to spiral in toward the Sun.

cjameshuff
2014-Mar-26, 01:13 AM
Magsails do have one advantage; as they move into the outer solar system, away from the Sun, their own magnetic field can expand to catch more solar wind particles and maintain a fairly even thrust, even at distances where the Sun is just a fairly bright star and a lightsail would be unable to even twitch.

On the other hand, they do the opposite as you get closer to the sun, shrinking down where a lightsail gets peak thrust.

Noclevername
2014-Mar-26, 01:24 AM
On the other hand, they do the opposite as you get closer to the sun, shrinking down where a lightsail gets peak thrust.

But they provide some shielding against cosmic ray particles.

So you have places for all three types of propulsion.

ShinAce
2014-Mar-26, 03:53 AM
If you start out in orbit around the Sun -- which of course all space probes do, -- it is possible to angle the sail so that the direction of thrust is opposite to the probe's orbital velocity (and approximately perpendicular to the Sun-probe line). That will act as a brake on the probe and cause it to spiral in toward the Sun.

Agreed.

publiusr
2014-Mar-30, 08:25 PM
Les Johnson is the go to guy on the subject
http://les-johnson.blogspot.com/2013/07/solar-sailing-to-stars.html
http://lesjohnsonauthor.com/

Sunjammer is his baby.

selvaarchi
2015-May-20, 07:49 AM
A shoebox-sized satellite will be launched in a few hours to bring to reality one of Carl Sagan's pet projects. Watch a young Carl Sagan talk about it on the Tonight Show (http://www.planetary.org/multimedia/planetary-tv/) way back in :rimshot: 1976.

Bill Nye of The Planetary Society is now championing it. Read more about it in Spaceflightnow.

http://spaceflightnow.com/2015/05/19/citizen-funded-cubesat-ready-to-go-solar-sailing/


A shoebox-sized satellite conceived and funded by members of the Planetary Society, an advocacy organization co-founded by Carl Sagan, is fastened to an Atlas 5 rocket for launch Wednesday to test one of the late celebrity-astronomer’s futuristic concepts for exploring the cosmos.

Sagan and other proponents of solar sailing pitch the technology as a way to cheaply glide through the solar system, harnessing energy from sunlight to slightly nudge a spacecraft toward its destination.

The solar sail prototype is going to an orbit a few hundred miles above Earth, where atmospheric drag will overpower any propulsion from the sun. A follow-up mission next year will try to use sun beams to change its orbit.

“We won’t fly high enough above the Earth’s atmosphere for solar sailing, due to atmospheric drag, but we’ll do critical tests of several systems over a 28+ day mission, including a zero-gravity test of our sail deployment sequence and attempt to snap pictures documenting the operation of the booms that support the sails,” the Planetary Society wrote on in a summary of the mission.

ravens_cry
2015-May-20, 09:20 AM
The Japanese already sent a probe to Venus using a solar sail (http://en.wikipedia.org/wiki/IKAROS). Despite being named IKAROS, a name just begging for trouble, :whistle:

selvaarchi
2015-May-20, 01:44 PM
The Japanese already sent a probe to Venus using a solar sail (http://en.wikipedia.org/wiki/IKAROS). Despite being named IKAROS, a name just begging for trouble, :whistle:

Thanks for highlighting that. I was under the impression this was the 1st test of the technology.

selvaarchi
2015-May-20, 03:14 PM
We have take off.

NEOWatcher
2015-May-20, 03:29 PM
Thanks for highlighting that. I was under the impression this was the 1st test of the technology.
Not only of the technology, but it's not even the first test from the Planetary Society.

From wiki, I compiled a terse list of previous solar sail attempts.
2001 Planetary Society, Cosmos 1. Rocket failure.
2005 Planetary Society LightSail. Rocket failure.
2006 JAXA, Solarsail Subpayload Satellite. Did not open completely.
2008 NASA, NanoSail-D. Launch failure.
2010 NASA, NanoSail-D2. Successful.
2013 Estonia, EstCube-1 (tether). Did not unwind.
Messenger also used the light sail effect to adjust its trajectory.

swampyankee
2015-May-20, 03:41 PM
The Japanese already sent a probe to Venus using a solar sail (http://en.wikipedia.org/wiki/IKAROS). Despite being named IKAROS, a name just begging for trouble, :whistle:

The Japanese used adhesives with better high temperature properties than did Daedalus

7cscb
2015-May-20, 04:22 PM
Not only of the technology, but it's not even the first test from the Planetary Society.

From wiki, I compiled a terse list of previous solar sail attempts.
2001 Planetary Society, Cosmos 1. Rocket failure.
2005 Planetary Society LightSail. Rocket failure.
2006 JAXA, Solarsail Subpayload Satellite. Did not open completely.
2008 NASA, NanoSail-D. Launch failure.
2010 NASA, NanoSail-D2. Successful.
2013 Estonia, EstCube-1 (tether). Did not unwind.
Messenger also used the light sail effect to adjust its trajectory.

Wow, The bad luck seems extraordinary. Rather commendable that they regardless persevered.

selvaarchi
2015-May-20, 07:44 PM
Not only of the technology, but it's not even the first test from the Planetary Society.

From wiki, I compiled a terse list of previous solar sail attempts.
2001 Planetary Society, Cosmos 1. Rocket failure.
2005 Planetary Society LightSail. Rocket failure.
2006 JAXA, Solarsail Subpayload Satellite. Did not open completely.
2008 NASA, NanoSail-D. Launch failure.
2010 NASA, NanoSail-D2. Successful.
2013 Estonia, EstCube-1 (tether). Did not unwind.
Messenger also used the light sail effect to adjust its trajectory.

Planetary Society does not talk about their past failures. Their write up concentrates on their current efforts.

http://www.planetary.org/blogs/jason-davis/2015/20150520-lightsail-liftoff.html


For the Planetary Society, the launch of LightSail marks the culmination of a six-year effort to send a solar sail CubeSat to space. The project began in 2009, but was temporarily sidelined by technical and funding challenges, as well as the need to find a sufficiently high-altitude flight. The spacecraft was originally built by San Luis Obispo-based Stellar Exploration, Inc. In 2014, Ecliptic Enterprises Corporation became the vehicle’s prime contractor, and Doug Stetson joined the team as project manager. Boreal Space serves as a contractor to Ecliptic. Testing and integration for LightSail occurs at Ecliptic as well as Cal Poly San Luis Obispo

NEOWatcher
2015-May-21, 01:28 PM
Planetary Society does not talk about their past failures. Their write up concentrates on their current efforts.

That's a shame. You would think a group that is trying to empower the public with space would explain the difficulties in spaceflight.

KaiYeves
2015-May-21, 03:04 PM
I'm very glad that this recent launch succeeded. Good luck, LightSail!

7cscb
2015-May-21, 04:34 PM
That's a shame. You would think a group that is trying to empower the public with space would explain the difficulties in spaceflight.

That is so true. It will get better but Risk and Failure are still a big part of Space Exploration. I am supposing that a space advocacy org may find it more convenient to stress the positive as it seeks to raise funds. But it does us a disservice in that a large number of enthusiasts seem to ignore the difficulties when advocating for exploration and so they adopt a tone of impatience.
There must be an interesting human story of passion, disappointment and perseverance. Maybe somebody else will tell it.

CJSF
2015-May-21, 05:28 PM
It's not like they're trying to cover up or hide past challenges. As far as I know, they've written about them in various blog posts and news items around the time the failures happened, and I'm pretty sure the membership newsletter/magazines that go out don't gloss over anything either. That they might choose the blog as a forward facing and optimistic place isn't surprising, though.

CJSF

publiusr
2015-May-23, 07:54 PM
That's a shame. You would think a group that is trying to empower the public with space would explain the difficulties in spaceflight.

It may be that they were embarrassed with using the Volna SLBM to begin with: http://en.wikipedia.org/wiki/Volna

Scratch that---Here is their report
http://www.planetary.org/blogs/guest-blogs/lou-friedman/ss_update_20050720.html

Now I seem to remember that they tried a second launch on a Volna, but the second try was listed as a Falcon 1 failure.

Here is what a solar sail looks like in space
http://www.planetary.org/multimedia/space-images/spacecraft/ikaros-sail-from-dcam2.html

selvaarchi
2015-May-23, 10:41 PM
It may be that they were embarrassed with using the Volna SLBM to begin with: http://en.wikipedia.org/wiki/Volna

Scratch that---Here is their report
http://www.planetary.org/blogs/guest-blogs/lou-friedman/ss_update_20050720.html

Now I seem to remember that they tried a second launch on a Volna, but the second try was listed as a Falcon 1 failure.

Their latest audio report has a brief mention of the Planetary Society LightSail rocket failure in 2005, as well as the Japanese probe that used a LightSail. I have posted it in the Dawn thread (http://cosmoquest.org/forum/showthread.php?57162-Progress-of-Dawn-in-the-solar-system&p=2290676#post2290676).

TJMac
2015-May-24, 02:22 PM
Risks and challenges

You may have heard this before, but it bears mentioning here: space is hard. Indeed, the entire LightSail project is a proof-of-concept experiment, and there is no guaranteed outcome. Despite genius engineering and painstaking work, failure could come at various stages—at launch, at release, during radio/attitude control testing, and at sail deployment. Or, we could just be delayed in our launch—a day, a week or a month or more due to technical, weather or other scheduling issues.

One of the great storylines in the LightSail saga is the project rising from the ashes (or in this case, the waters) like the Phoenix of Greek mythology. The Planetary Society lost our first solar sailing prototype spacecraft, Cosmos 1, in June 2005 (almost exactly 10 years ago!) when the Russian Volna rocket that was lifting it into orbit failed and went off-course, landing somewhere in the Barents Sea. The Atlas V and SpaceX Falcon Heavy rockets promise more reliable rides to the stars, but things can always take a turn because, well, space is hard.

Thats from the Kickstart site https://www.kickstarter.com/projects/theplanetarysociety/lightsail-a-revolutionary-solar-sailing-spacecraft

I've been fascinated for a while about this project. It would be great to be more involved, but at least I'll get a sweet poster out of my donation. I already picked a spot to hang it. :D

All updates so far have been pretty positive, so hopefully, they got past the "space-is-hard" gremlin this time.


TJ

publiusr
2015-May-24, 07:11 PM
So let's say a Block 2 SLS with a hydrogen upper stage to get it out of Earth-moon (or a Musk BFR with a non-hydrolox upper stage) but, say, 80 tons of the current material in free space. That would open up to, say, a mile or so on a side?

selvaarchi
2015-May-27, 09:26 AM
Problem - Planetary Society LightSail has been hit with a software glitch. Read all about it.

http://www.planetary.org/blogs/jason-davis/2015/20150526-software-glitch-pauses-ls-test.html


The Planetary Society’s LightSail test mission is paused while engineers wait out a suspected software glitch that has silenced the solar sailing spacecraft. Following a successful start to the mission last Wednesday, LightSail spent more than two days sending about 140 data packets back to Earth.

But the long Memorial Day weekend here in the United States offered no respite for the LightSail team, as they scrambled to figure out why the spacecraft's automated telemetry chirps suddenly fell silent. It is now believed that a vulnerability in the software controlling the main avionics board halted spacecraft operations, leaving a reboot as the only remedy to continue the mission. When that occurs, the team will likely initiate a manual sail deployment as soon as possible.

CJSF
2015-May-27, 12:21 PM
A software glitch they seem to have been aware of, but could do nothing about. I think hoping for a cosmic ray hit for a reboot is a bit desperate... :-/

CJSF

Extravoice
2015-May-27, 12:47 PM
A software glitch they seem to have been aware of, but could do nothing about.CJSF

It sounds like they became aware of it late in the game, and were preparing a fix (or at least a work-around) when the problem occurred.
I wonder if they are certain an over-sized file is the problem. It sure highlights the importance of verification testing.


I think hoping for a cosmic ray hit for a reboot is a bit desperate...
Maybe they should have included a watchdog timer. (Says the Monday-morning quarterback.)

selvaarchi
2015-Jun-01, 08:50 PM
The little one has called home after 8 days. So happy days are back again at the Planetary Society. Two reports below. 1st one on the call back and the next one talking about the sail deployment coming up this Wednesday 3ed June.

http://www.planetary.org/blogs/jason-davis/2015/20150530-lightsail-phones-home.html


The Planetary Society’s LightSail test spacecraft reported for duty this afternoon, heralding the end of an uneasy silence caused by a suspected software glitch. At 5:21 p.m. EDT (21:21 UTC), an automated radio chirp was received and decoded at the spacecraft's Cal Poly San Luis Obispo ground station. Another came in eight minutes later at 5:29 p.m. The real-time clock on board the spacecraft, which does not reset after a software reboot, read 908,125 seconds—approximately ten-and-a-half days since LightSail’s May 20 launch.

http://www.planetary.org/blogs/jason-davis/2015/20150531-lightsail-possible-tuesday-deploy.html


Update, June 1: Tomorrow's solar sail deployment has been rescheduled to Wednesday to allow for additional image capture and downlink testing. A timeline will be posted as soon as it is confirmed.

LightSail is almost ready for its moment in the sun.

This afternoon, mission managers gave the go-ahead for a manual solar sail deployment as early as Tuesday, June 2 at 11:44 a.m. EDT (15:44 UTC), providing the spacecraft completes an arduous set of Monday preparations. Since waking up Saturday after eight days of silence, the spacecraft has been busy sending telemetry back to Earth, snapping test images and preparing itself for sail deployment.

Squink
2015-Jun-01, 10:44 PM
Three cheers for cosmic ray induced reboots!

KaiYeves
2015-Jun-02, 01:11 AM
Phew! Let's hope for smooth sailing from here on out!

CJSF
2015-Jun-02, 04:53 AM
Phew! Let's hope for smooth sailing from here on out!

Hahaha! I see what you did there!

Agreed!

CJSF

selvaarchi
2015-Jun-05, 05:16 AM
It has gone silent for the 2nd time :(

http://www.planetary.org/blogs/jason-davis/2015/20150604-lightsail-silent-again.html


The LightSail test spacecraft has fallen silent for a second time, less than a day after completing what appeared to be a successful solar panel deployment. Mission managers believe the CubeSat's batteries are in a safe mode-like condition designed to protect the electronics until power levels are safe for operations.

In an e-mail summary sent this afternoon, mission manager David Spencer said before contact was lost, LightSail’s batteries did not appear to be drawing current from the solar arrays; nor were they properly shunting power to the spacecraft’s subsystems.

"Following solar panel deployment," he wrote, "it was noticed that all of the battery cells were drawing near zero current. This indicated that the batteries were likely in a fault condition stemming from the solar panel deployment event."

Extravoice
2015-Jun-05, 10:21 AM
Nuts. Things where looking up for a while.


Sent from my iPhone using Tapatalk

KaiYeves
2015-Jun-05, 03:18 PM
Dangit!

Squink
2015-Jun-05, 07:51 PM
Dangit!If Bill Nye were up there, he could fix it.

01101001
2015-Jun-07, 04:24 AM
It's back again. 7/8 batteries charging. Unfurl Sunday 2:02pm EDT -- quick before it glitches again.
http://www.planetary.org/blogs/jason-davis/2015/20150506-lightsail-wakes-second-time-1.html

selvaarchi
2015-Jun-07, 06:58 AM
:clap: Hope they do the full deployment.

Extravoice
2015-Jun-07, 02:16 PM
I hope they are able to collect enough data to identify and prevent these issues in the future. And I'm keeping my fingers crossed for a sail unfurling this afternoon


Sent from my iPhone using Tapatalk

publiusr
2015-Jun-07, 07:01 PM
Drat!
http://mashable.com/2015/06/07/bill-nye-lightsail-spacecraft/

This was released as a cubesat from the X-37--so I'm thinking it was packed perhaps a bit too tightly.

Hoping for Sunjammer to get it right: http://www.cosmicarchive.com/t-About-Sunjammer.aspx

The wiki has it as cancelled but here there is a call for a 2017 launch:
http://www.cosmicarchive.com/t-Launch-Schedule.aspx

01101001
2015-Jun-07, 09:55 PM
Drat!
http://mashable.com/2015/06/07/bill-nye-lightsail-spacecraft/


Update: Second attempt was a success.

Lightsail just takes two tries at every phase.

Squink
2015-Jun-10, 11:39 AM
Planetary Society: LightSail Test Mission Declared Success; First Image Complete (http://www.planetary.org/blogs/jason-davis/2015/20150609-lightsail-test-mission-success.html)
LightSail captured this image of its deployed solar sails in Earth orbit on June 8, 2015.
...
it is believed the second photograph may include a view of Earth.

Squink
2015-Jun-17, 02:02 AM
Never got the second photo:

LightSail Test Mission Declared Success: LightSail Test Mission Ends with Fiery Reentry (http://www.planetary.org/blogs/jason-davis/2015/20160615-lightsail-test-mission-ends.html)

A complete image of the spacecraft’s solar sails was downloaded on June 9, confirming the mission’s primary objective of sail deployment had been met. But before engineers could get a picture from the opposite-side cameras, LightSail’s radio began transmitting a continuous, nonsensical signal, and the spacecraft stopped responding to commands.

selvaarchi
2015-Jun-26, 04:25 PM
Another solar sail effort is being readied for a July departure. It is called the DeorbitSail project and led by Surrey Space Centre at the University of Surrey in Guildford, United Kingdom. If you have not guessed it by now, DeorbitSail is a small satellite mission that will launch and deploy a roughly 13 foot by 13 foot (four-by-four-meters), four-quadrant sail to showcase rapid deorbiting.

http://www.leonarddavid.com/deorbitsail-ready-for-sendoff/


Following in the wake of the Planetary Society’s LightSail-A mission, another solar sail effort is being readied for a July departure.

Boxed up and delivered to India last month, the DeorbitSail mission is among a number of payloads to be rocketed into space from the Satish Dhawan Space Center, Sriharikota, India.

The DeorbitSail project is a collaboration to build a 3 unit (3U) CubeSat-sized satellite with a deployable sail that will demonstrate rapid deorbiting.

publiusr
2015-Jun-27, 08:13 PM
I'd kinda like to see one attached to a tether---kite-sail

selvaarchi
2019-Jul-02, 12:30 PM
Another solar sail effort is being readied for a July departure. It is called the DeorbitSail project and led by Surrey Space Centre at the University of Surrey in Guildford, United Kingdom. If you have not guessed it by now, DeorbitSail is a small satellite mission that will launch and deploy a roughly 13 foot by 13 foot (four-by-four-meters), four-quadrant sail to showcase rapid deorbiting.

http://www.leonarddavid.com/deorbitsail-ready-for-sendoff/

SpaceX sent it up. Now LightSail 2 has called home.

http://www.planetary.org/blogs/jason-davis/first-contact-lightsail-2.html


The Planetary Society's LightSail 2 spacecraft sprung loose from its Prox-1 carrier vehicle as planned today, and sent its first signals back to mission control at Cal Poly San Luis Obispo in California.

The CubeSat, about the size of a loaf of bread, was scheduled to leave Prox-1 precisely 7 days after both spacecraft successfully flew to orbit aboard a SpaceX Falcon Heavy rocket. Following deployment from its spring-loaded enclosure known as a P-POD, LightSail 2 deployed its radio antenna and began transmitting health and status data, as well as a morse code beacon indicating its call sign. The mission team received LightSail 2's first signals on 2 July at 01:34 PDT (08:34 UTC), as the spacecraft passed over Cal Poly.

selvaarchi
2019-Jul-08, 03:28 PM
"Here are the First Pictures of Earth from LightSail 2"

http://www.planetary.org/blogs/jason-davis/lightsail-2-first-pics.html


The first pictures from The Planetary Society's LightSail 2 mission are on the ground!

Flight controllers successfully deployed the CubeSat's dual-sided solar panels Friday evening, as it flew south of mission control at Cal Poly San Luis Obispo in California. Pictures taken moments later from the spacecraft’s solar panel-mounted cameras show a crescent Earth, as LightSail 2 heads into orbital sunset.

selvaarchi
2019-Jul-10, 02:01 PM
"LightSail 2 Team to Conduct More Testing before Sail Deployment"

http://www.planetary.org/blogs/jason-davis/ls-2-more-testing.html


The LightSail 2 mission team has delayed deployment of the spacecraft’s solar sail until at least 21 July 2019 to conduct additional attitude control system testing and potentially update the spacecraft’s flight software. LightSail 2 remains stable and healthy in orbit, and returned another picture to mission control at Cal Poly San Luis Obispo in California.

selvaarchi
2019-Jul-18, 03:14 PM
"LightSail 2 Team Continues Tweaks and Tests for Sail Deployment"

http://www.planetary.org/blogs/jason-davis/lightsail-2-team-continues-tweaks-tests.html


The LightSail 2 mission team is continuing to tweak and test the spacecraft in preparation for solar sail deployment, which is scheduled for no earlier than 21 July 2019. Flight controllers successfully uploaded a software patch that refined the operation of the spacecraft's electromagnetic torque rods, which are responsible for keeping LightSail 2 stable as it circles the Earth. Spare bandwidth during ground station passes has also allowed for the downlink of 2 new high-resolution images.

publiusr
2019-Jul-18, 11:20 PM
SpaceX's super heavy/SLS could deploy a sail weighing many tons that could open up to several square kilometers--if enough of the material can be made--now you would have something.

selvaarchi
2019-Jul-25, 04:08 PM
"LightSail 2 Successfully Deploys Solar Sail"

http://www.planetary.org/blogs/jason-davis/ls2-deploys-sail.html


The Planetary Society’s LightSail 2 spacecraft has successfully deployed the large, aluminized Mylar sail it will use to raise its orbit solely with sunlight.

Flight controllers at Cal Poly San Luis Obispo in California commanded the spacecraft to deploy its solar sails yesterday at about 11:47 PDT (18:47 UTC). Images captured during the deployment sequence and downloaded today show the 32-square-meter sail, which is about the size of a boxing ring, deploying as the spacecraft flew south of the continental United States.

selvaarchi
2019-Aug-01, 01:10 PM
LightSail 2 declared a success :clap

https://www.france24.com/en/20190801-flight-light-mission-accomplished-lightsail-2

[QUOTE]Mission accomplished: the Planetary Society announced Wednesday that its LightSail 2 spacecraft, which was launched last month, had successfully raised its orbit using only the power of photons from the Sun.

The team behind the $7 million crowd-funded venture said they had demonstrated a proof of concept for a new form of propulsion that could one day transform deep space exploration by doing away with the need for expensive rockets and fuel.

"In the past four days the spacecraft has raised its apogee, or orbital high point, by about 1.7 kilometers (one mile) attributable to solar sailing," said Bruce Betts, LightSail 2 program manager.[QUOTE]