Posted on by Elizabeth Howell

How the Space Shuttle Killed an American Halley’s Comet Mission

Halley's Comet, as seen by the European Giotto probe. Credit: Halley Multicolor Camera Team, Giotto Project, ESA
Halley's Comet, as seen by the European Giotto probe. Credit: Halley Multicolor Camera Team, Giotto Project, ESA

NASA missed the chance to visit Halley’s Comet in 1986 when the famed sentinel swung close to Earth, as it does every 76 years. Luckily for history, the Europeans flew Giotto past it on this day (March 13) in 1986, and some other nations sent their own probes.

The full story of NASA’s withdrawal is in Bruce Murray’s Journey Into Space: The First Three Decades of Space Exploration. Murray, the former director of the Jet Propulsion Laboratory, has chapters upon chapters on Halley, but here are some notable highlights.

First of all, there were at least three initiatives for NASA to send a mission to the famed comet. The missions below are in chronological order, and it appears it was only when the preceding one was killed that the next was envisioned:

– Solar sail. This mission would use the power of the solar wind — bits streaming from the sun — to bring a spacecraft within Halley’s gravitational influence. In fact, the spacecraft would stay with Halley as it whisked out of the solar system and would return (long dead) when Halley came back in 2061.

– A rendezvous with Comet Tempel 2. Another idea would see a spacecraft swing close to Comet Tempel 2 but also have a probe that would take a picture of Halley from a distance. NASA also considered splitting the mission in two to meet annual budgetary requirements, but the Comet Science Working Group was cool to the idea. There also was some thought about bringing the Europeans into this mission, but that never worked out.

– Galileo-type hardware. A third initiative had the Jet Propulsion Laboratory envisioning a distant flyby of Halley, basically using similar types of parts that flew in a spacecraft (called Galileo) to Jupiter.

All three of these initiatives fell to budget cuts during the 1970s and 1980s. What caused the budget cuts? In large part, the space shuttle program. To be sure, the shuttle was an impressive piece of hardware, and we are not doubting what it contributed to the construction of the International Space Station and to human spaceflight in general. But it was a large project and in those tight times, something had to give.

Perhaps the most interesting cancellation came in 1979, when NASA administrator Robert Frosch and his deputy went to President Jimmy Carter’s office to plead for the case of two projects: a solar electric propulsion system that would eventually power the Halley-Tempel 2 mission, and the Compton Gamma Ray Observatory (which flew into space, after many delays, in 1991).

Carter, according to Murray, was reading a book on black holes penned by Walter Sullivan of the New York Times. (We’re assuming it’s the 1979 book Black Holes: The Edge of Space, the End of Time.) When presented with the options, Carter said he was “partial to the gamma-ray thing because of this connection with the black-hole problem.”

That signaled the beginning of the end for NASA’s Halley-Tempel 2 mission.

Posted on by Elizabeth Howell

3 Comets That Fizzled

An artist's conception of a comet. Credit: NASA/JPL-Caltech

Take a dirty snowball in space and hurl it towards the Sun. I dare you… and then make a prediction as to how that will look.

This is the problem comet scientists face when talking about how bright a comet will appear from Earth. They’re imaging a conglomerate of dust, ice and other materials millions of miles away. After figuring out where the comet will go, then they have to predict how it will behave.

It’s a science, to be sure, but an unpredictable one. That’s why it’s so hard to figure out how Comet ISON will fare when it gets closer to the Sun in November 2013. It could blow into pieces before arriving. It could break up when it gets close to the Sun. Or, it could live up to wildest expectations and shine so brightly you’ll be able to see it in daylight.

Veteran comet-gazers can name a few visitors that didn’t perform as well as predicted. Michael Mumma, who is with the NASA Goddard Space Flight Center’s solar system exploration division, was the lead for the agency’s scientific campaign on many comets of the past few decades. In an e-mail to Universe Today, he shared what made three comets less spectacular than predictions.

Comet Kohoutek (1973)

Comet Kohoutek in 1973. Credit: NASA/University of Arizona
Comet Kohoutek in 1973. Credit: NASA/University of Arizona

Billed by some as the comet of the century, Comet Kohoutek was predicted to pass close to the Sun after it was discovered in March 1973. NASA initiated “Operation Kohoutek” to keep an eye on the comet from a network of observatories in the sky, on the ground and even telescopes in mid-air.

Mumma joked that Kohoutek was a great career launcher for him, as a spectrometer that searched for ammonia ended up getting sustained funding for further development. But the comet was a visual disappointment, he acknowledged.

“The hype surrounding Comet Kohoutek was inspired by two predictions of its possible brightness, made by a recognized senior comet scientist. The NASA spokesman chose to promote the brighter of the two, that predicted the comet would become as ‘bright as the full Moon’. He usually mentioned (softly) that we couldn’t be certain it would actually brighten that much – but the press usually ignored that disclaimer,” Mumma wrote.

“Actually, the comet really did fizzle, failing to reach even the fainter estimate – probably because at discovery it was far from the Sun and activated by something other than water ice. Under those circumstances, any prediction was bound to be highly uncertain.”

Halley’s Comet (1986)

Halley's Comet in 1986. Credit: NASA
Halley’s Comet in 1986. Credit: NASA

Halley’s is the most famous periodic comet, meaning that it returns to the inner solar system over and over again. Its bright appearance made it show up repeatedly in the historical record, most famously in the Bayeux Tapestry after it arrived in 1066 shortly before William the Conquerer successfully led the Norman Conquest of England. However, astronomers in each era saw the comet’s appearance as separate, unpredictable events.

English astronomer Edmond Halley, in examining the astronomical record in 1705, supposed that a comet with similar properties that appeared every 75 years or so was probably the same comet. Ever since then, astronomers and the public alike eagerly await each appearance. The 1910 visit was particularly spectacular, making the press set high expectations for 1986. However, the comet was much further away from the Sun in the 1980s and was fainter.

According to Mumma, the comet did not actually fizzle. Many press reports just got the brightness of the comet wrong, leading the public to believe the comet was less spectacular than predicted.

“It was a bright comet, just as scientists predicted. However, it was much brighter in the southern hemisphere  than in the northern, as predicted. From Christchurch (New Zealand), and again from Cairns (Australia), it was large and the brightest object in the sky – easily seen with the unaided eye.”

As a scientific sidenote, Mumma’s team probed the comet with NASA’s Kuiper Airborne Observatory and, using infrared fluorescence spectroscopy that Mumma developed, found water for the first time in a comet.

Comet Austin (1990)

A negative image of Comet Austin. Credit: European Southern Observatory
A negative image of Comet Austin. Credit: European Southern Observatory

In 1989, Sky & Telescope published a cover article on Comet Austin with the eye-catching headline: “Monster Comet is Coming!” As with Halley, many people anticipated this would be a bright comet, easily visible with the naked eye. In the book Hunting and Imaging Comets, United Kingdom amateur astronomer Martin Mobberley pointed out it was a great object in telescopes or binoculars, but not so much with the eye alone.

“Austin was less bright than some had predicted, but it was bright enough to permit major scientific successes,” Mumma added in his e-mail to Universe Today. “My team detected CO (carbon monoxide) and methanol in that comet, among the first detections of these molecules in comets at infrared wavelengths.”

All in all, these comets show that it’s really hard to figure out what they look like when they get by Earth. This means that nobody knows exactly how ISON will behave until it’s almost upon us.