Concerning space missions, there’s always something happening in space. Most of it is ‘routine’ in the sense that what happens was expected and a normal part of the mission. Re-supply of the International Space Station generally falls into that category (except a couple of weeks ago when the resupply vehicle missed the station on the first try). There are a lot of missions currently underway; some just getting started, others have been at it for years. They all generate events of one kind or another. In the last week or so, there are two pieces of news from space missions that deserve more attention, not only because they represent successes, but because they were difficult first-of-a-kind achievements: The Rosetta flyby of Lutetia, and the IKAROS solar-sail uses photon propulsion.
The asteroid Lutetia with Saturn (the background dot)…..Credit: ESA, MPS Osiris Team
The Rosetta probe flyby of the asteroid Lutetia
The spacecraft Rosetta, launched in 2004 by the European Space Agency (ESA) was maneuvered into position for a flyby of the asteroid Lutetia. The closest approach point was to be 3162 m (10,374 ft) from the surface of the relatively large asteroid. The flyby was unique on several grounds:
1. It was the first flyby of Lutetia and the largest asteroid yet visited (longest axis 126 kilometers, 78.29 miles).
2. The camera used was of exceptionally high resolution (2000 pixel frame), which yielded many extremely fine photographs.
3. The flyby was available through ‘live feed’ on the Internet as it was being observed at ESA headquarters on Earth.
Almost going without mention is the extraordinary accuracy of the celestial navigation and the obvious reliability of the Rosetta probe. One of the images captured by Rosetta during the flyby just happened to also include another heavenly body – the unmistakable ringed planet Saturn. Such juxtapositions are extremely rare. Of more immediate scientific interest will be the crater pocked surface of Lutetia for analysis of the geology and possible history of the asteroid.
Rosetta is now on its uninterrupted way to a rendezvous with the comet Churyumov-Gerasimenko in 2014. Much of the next four years will be spent in ‘deep hibernation’ to conserve energy during another very long swing around the sun in order to gain matching speed with the comet.
The IKAROS lightsail is using photon propulsion
The spacecraft IKAROS (Interplanetary Kite-craft Accelerated by the Radiation Of the Sun) launched in May of this year by Japan’s Aerospace Exploration Agency (JAXA) has already passed several critical stages (besides all the usual difficulties of escaping Earth’s gravity well), such as deployment of its solar sail propulsion system. On July 12, JAXA confirmed that the spacecraft is now the first ever spacecraft to use ‘solar wind pressure’ – the flow of photons that constantly stream away from the Sun – as its source of propulsion energy. That photons could have ‘pushing power’ is not a surprise, of course; this has been proven theoretically and experimentally many times. However, this was the first time with a real, in-space, solar sail.
The sail is a 200-square-meter sheet made of a polyimide resin only 0.0075 millimeter thick. It has a solar array and eight LCD cells imbedded in the sheet. The sail has no supporting structure and is kept flat by the spinning motion of the spacecraft. According to measurements taken by using Doppler radar, the sail is now generating a force of about 1.12 millinewtons (0.0002 pounds of force). This does not provide for much acceleration, but the energy is free and inexhaustible. Currently IKAROS is about 11 million kilometers from Earth and heading toward the planet Venus. It has one more big test, to demonstrate that the combination of solar-sail and photon propulsion can be used for navigational maneuvering.
There have been other attempts at a working space-sail (with a notable failure of the COSMOS-1 in 2001). The goal is to prove that solar wind pressure is sufficient for certain kinds of spacecraft that have plenty of time for long-duration but ultimately powerful acceleration.