Today is, I gather, the holiday of something love-related?
It sure is. Asteroid “Eros” (named for the Greek god of love) had, twenty-five years ago today, been the site of a space “first”- the first orbiting of an asteroid (or other small body). The NEAR Shoemaker space probe (that’s Near-Earth Asteroid Rendezvous, later with Eugene Shoemaker’s commemorative naming) fired its main engine to brake itself into Eros orbit on Feb. 14, 2000.
But it almost didn’t happen, on multiple levels. First, NEAR was the first true deep-space probe in NASA’s new Discovery Program of faster, cheaper Solar System probes. (Lunar Prospector, technically, launched second but reached its target first, then ran its paces before 2000.) The Discovery Program was a response to the size, cost, mission length, and complexity growth of prior probes (joked to be “Battlestar Galacticas”). One of the key differences of Discovery was that each project could be credibly threatened with cancellation- each is specifically organized, and continually reminded, that it is not too big to fail. The budget ax is ready and waiting if mission managers screw it up. With the exception of Clementine, these small, fast projects were rare (and Clementine was Navy, not NASA).
Second, NEAR itself almost screwed it up. The original mission plan called for the probe to rendezvous with, and brake into orbit around, Eros in December of 1998. However, a spacecraft fault caused the engine burn to fail. Ground ops staff rushed to salvage the mission; they devised a plan where, after a deep-space maneuver (a nontrivial engine burn), NEAR would be set up to loop around the Sun once more, then enter Eros orbit roughly 13 months later.
Fortunately, that worked. NEAR and Eros approached each other, then rendezvoused after almost an entire orbit, and then the real Orbit Insertion Manuever occurred according to plan. We had achieved orbit about a non-planet (and non-star, the Sun already has all of us) for the first time ever. NEAR would go on to study a small body for over one (Earth) year.
Third, the faster-cheaper approach had other risks. To save cost, the NEAR mission’s gamma-ray instrument (GRS, Gamma-Ray Spectrometer) was mounted on a bracket to the main spacecraft structure. That’s a bracket, not a boom. This cost-saving measure (a boom is a deployable, a mechanism) turned out to have an impact on the mission results, at least at first. The GRS detected the spacecraft’s emissions, but Eros gamma rays, not so much. The gamma signal was clearly, obviously contaminated.
Fourth (?), the decision was made at the end of the mission to try a high-risk, high-reward maneuver. Mission operators would try to land NEAR on Eros. This, despite the fact that the spacecraft had never been designed to land, had no true landing engine, and didn’t even have landing legs or other structures. On Feb. 12, 2001, the NEAR probe braked out of orbit, and reached the asteroid’s surface. On its way down, the images from the NEAR camera would be closer and sharper than anything from orbit, even the later, closer orbits. And yet, on touchdown, the landing was slow enough (because Eros’ gravity is low enough) that NEAR survived- survived without any prior preparation for landing! Once on the surface, the “range” for the Gamma-Ray Spectrometer was effectively zero. (We’re still not sure if the landing occurred so that the structure planted the GRS into Eros’ regolith.) With Eros right up to the GRS instrument, we finally got good gamma-ray data (though only of that one spot, of course). February 14th, then, is also the anniversary of, um, still operating on the surface of an asteroid, 24 years ago.
Happy anniversary, NEAR, and congratulations, NEAR ops team and entire NEAR project!