America Forgot How to Talk to Its Zombie Spaceship

One of our greatest space explorers is coming home — but we no longer speak its language.

National Journal
Alex Brown
Feb. 12, 2014, midnight

A long-lost, pi­on­eer­ing space­ship — still func­tion­al thanks only to chance and hu­man er­ror — is com­ing home for the first time in three dec­ades. It wants to ex­plore new worlds. But we’ve for­got­ten how to talk to it.

ISEE-3 — short for In­ter­na­tion­al Sun-Earth Ex­plorer — was launched in 1978, ex­ecut­ing a pair of sci­entif­ic mis­sions and a ground­break­ing in-space man­euver that’s still used to this day. “It’s def­in­itely a spe­cial space­craft in the his­tory of plan­et­ary ex­plor­a­tion,” the Plan­et­ary So­ci­ety’s Emily Lak­dawalla said. The satel­lite comes in at just over 850 pounds, but its con­tri­bu­tions to sci­ence have been sig­ni­fic­ant.

As it nears Earth — it will ar­rive in Au­gust — we’ll have our best op­por­tun­ity in 31 years to re­dir­ect it on an­oth­er mis­sion. But that won’t hap­pen. The space­craft was long ago giv­en up for dead, and as a res­ult, the ‘70s-era tech­no­logy we used to talk to it was scrapped. The Deep Space Net­work lost the prop­er trans­mit­ters in 1999.

That should have been the end of the story. When we stopped talk­ing to the ISEE-3, it was sup­posed to stop talk­ing to us. But in 2008, someone re­membered they’d neg­lected to tell the ship to turn off its trans­mit­ters. A quick sig­nal search re­vealed the craft was still in its pre­cise or­bit with 12 of 13 sci­entif­ic in­stru­ments still op­er­a­tion­al.

“Or­din­ar­ily when NASA is done with a mis­sion, they send a com­mand to turn off the trans­mit­ter,” Lak­dawalla said. “This was kind of a mis­take, the fact that this trans­mit­ter is still op­er­at­ing.” More im­press­ive is the fact that its 30-plus-year-old in­stru­ments still seem to be in work­ing or­der. “As far as we know, this thing is work­ing ex­tremely well giv­en its age — and it has a lot of use­ful sci­entif­ic in­stru­ments.” The prob­lem is that we can’t tell ISEE-3 to give us a com­plete pic­ture of its health “be­cause we can’t cur­rently speak its lan­guage.”

If we could talk to ISEE-3, we could use its Earth ap­proach this sum­mer as a jump­ing-off point to send it comet-hunt­ing (it be­came the first space­craft to fly past a comet in 1985). It’s equipped to meas­ure plas­mas, en­er­get­ic particles, waves, and fields.

Some want to crack the his­tory books and fig­ure out how to re­build the trans­mit­ter ne­ces­sary to once again talk to our lonely space­ship. Why waste a re­source that we’ve already put in space? But NASA says that would prove too ex­pens­ive. “They thought it would [cost] so much that it wasn’t worth spend­ing the staff time to get the es­tim­ate,” Lak­dawalla said. “NASA has lim­ited re­sources, and they have to fo­cus on the ones that are pro­du­cing the best sci­ence right now.”

So ISEE-3’s con­tri­bu­tions will be lim­ited to its past. They’re not in­sig­ni­fic­ant.

The ship’s most not­able break­through was us­ing a Lag­rangi­an point to change its tra­ject­ory, a move that had nev­er been done be­fore. What’s a Lag­rangi­an point? Lak­dawalla com­pares it to the mid­point of a dumb­bell, a spot in which grav­it­a­tion­al pull is nearly bal­anced in both dir­ec­tions. Five such loc­a­tions ex­ist in the Earth and sun’s or­bit­al con­fig­ur­a­tion, al­low­ing space­craft to “park” and con­serve en­ergy. ISEE-3 was the first to use L1, or­bit­ing con­tinu­ously between Earth and the sun to mon­it­or sol­ar wind.

In 1982, when ISEE-3 was re­as­signed to comet-hunt­ing duty, it was able to use L1 to eas­ily re­pos­i­tion it­self in­to or­bit around the sun. “If you nav­ig­ate a space­craft to one of those [Lag­rangi­an] points, you get an op­por­tun­ity to change the space­craft’s path a great deal with very little en­ergy,” Lak­dawalla said. “This par­tic­u­lar tech­nique was pi­on­eered by ISEE-3.”

It stud­ied Comet Gi­ac­obini-Zin­ner’s plasma tail in 1985, then joined the “Comet Hal­ley Ar­mada” in 1986 when earth­bound sci­ent­ists be­came fix­ated on the ap­proach­ing comet. It’s re­mained in he­lio­centric or­bit since then, gradu­ally get­ting closer to Earth as it main­tains a slightly faster or­bit. It’s com­pleted 31 or­bits of the sun dur­ing the same time Earth has com­pleted 30.

Come Au­gust, ISEE-3 will fi­nally near its ter­restri­al ori­gins again, caus­ing its or­bit to change — but we won’t be able to tell it where to go next.

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