# Are there any space probes or landers which regained communication after being lost?

Recently, ISRO Vikram lander of Chandrayaan 2 lost its communication just before 2.1 km from lunar surface. ISRO staff still trying to regain the signals.

Are there any space probes/landers which regained communication after being lost like this one?

• Most interplanetary missions have been 'lost' for at least short periods due software mishaps of various sorts, tried to do a search but not finding any summaries. – GremlinWranger Sep 8 '19 at 11:20
• I am reading now that they have at least re-imaged the lander, which is a better outcome than most such cases. Stay tuned. – Oscar Lanzi Sep 8 '19 at 18:12
• To clarify regarding what @GremlinWranger said, are you mainly interested in cases where the "lost" status was unexpected and interpreted as likely-permanent before communication was regained? – R.. GitHub STOP HELPING ICE Sep 8 '19 at 22:44
• Remember V'Ger? – user29195 Sep 9 '19 at 13:51

Well, it is very common indeed to regain communications with a space probe after losing contact. In fact, communications are generally not continuous for the entirety of any mission. These are generally planned, for example

• This happened with almost each and every satellite at the beginning of the space age. Both the former USSR and the US are huge countries, but still their probes periodically went radio silent when on the other side and hemisphere of the planet (since neither had access to antennas outside of their territories). Even for manned missions like Yuri Gagarin's Vostok 1 you can see the several minutes long interruptions and contact recoveries in the communications log. This is the reason why both the USSR and the US built satellite tracking ships and moved them to locations in the ocean where they could have continuous coverage of the transmitting signals of their satellites.

• When Mars goes behind the Sun (from Earth's perspective) signals with the orbiters and landers are lost and communications are re-established weeks later (when the line of sight with Mars stops crossing the radio-interfering region of the solar corona).

• The plasma generated on any atmospheric entry around a probe acts like a Faraday cage, cutting off any incoming or outgoing signal for several minutes. Contact is usually lost when cosmonauts and astronauts come back from the ISS. It was lost for the Vostok, Apollo, and Gemini missions. It is usually lost for Martian probes during atmospheric entry (the so-called "7 minutes of terror") and it has also happened with the European Huygens probe when it entered Titan's atmosphere.

• A communications blackout is also common for special maneuvers. For example during Cassini's ring-plane crossing maneuvers the antenna was used as a shield against possible microscopic impacts, and thus it couldn't point to Earth for several minutes.

• During the Apollo missions, astronauts had communications blackouts due to passing behind the Moon while in orbit. The Moon shields any kind of radio signals from Earth, and thus they went silent for 10 to 60 minutes. This was the case for Apollo 8 and Apollo 11.

• For many artificial satellites around Earth, and in particular for geostationary satellites, the Sun can saturate the radio flux so much that no signal from the satellite can be noticed, thus making communications impossible. This happens only when the satellite ends up been in the line of sight of the Sun. These blackouts can cut communications, GPS, internet connectivity and other logistics.

• For long trips in interplanetary space, any hibernation period for the spacecraft is usually scheduled. This was the case for the New Horizons probe on its way to Pluto. For a few months the probe was silent. This is also done when energy consumption has to be managed, such as with the hibernation period of the Kepler space telescope.

In all these cases signal is lost and recovered in a controlled fashion, with the exact moments of contact lost and recovery perfectly known and planned. But I guess you are asking for cases where contact was unintentionally lost and then recovered. There are also some interesting cases where that happened:

Here you have a picture taken from Rosetta of the Philae lander (in the center-extreme-right side of the image) photographed in the shadow cast by the walls of the crack:

• Your first group aren't cases of communication being "lost", they are simply planned/known interruptions. – jamesqf Sep 8 '19 at 17:32
• In the case of the New Horizons loss, communication was re-established within 90 minutes -- with the backup computer. Not good enough, they had to repair the main computer crash and get the command load back online, all within three days because of the way the flyby was scheduled. Stern and Grinspoon's account of what they did over those three days, referenced in this answer, is recommended for all who visit this site. – Oscar Lanzi Sep 8 '19 at 18:09
• "A communications blackout can only mean one thing: An invasion!" (someone in the retinue of Princess Amygdala). Seriously a good answer. One should add that communication loss with gear that touched down is generally more ominous (crash, electrical malfunction, solar panel unusable with no way of recovery) than communication loss with space probes in flight (generally software error, which causes the probe to go to safe mode and reboot, then seek out a signal from Earth while taking care to keep its panels correctly oriented) – David Tonhofer Sep 8 '19 at 18:44
• The first link in the "The IMAGE satellite..." bullet point is broken (it's literally http://scott%20tilley/). An edit is pending so I can't try to fix it... – T.J. Crowder Sep 9 '19 at 8:21
• Not a probe or lander, but a 'lost contact' satellite example is the amateur radio satellite AMSAT-OSCAR 7. Launched in 1974 with a three-year anticipated lifetime, it went silent in 1981 due to battery failure. In 2002 a battery went open circuit and the satellite resumed service under solar power. It is still operational 17 years later. – Leorex Sep 9 '19 at 15:49

Are there any space probes\landers which regain communication after being lost?

## IMAGE

Contact was lost with IMAGE on December 18, 2005, 07:39 UTC and it was detected again by amateur satellite hunter Scott Tilley on January 20, 2018. You can read more about it in that Wikipedia article and this answer and this answer

## SOHO

SOHO was nearly lost. Communications was severely impacted by a loss of attitude control and antenna pointing. It was touch-and-go for a while:

From Is this what station keeping maneuvers look like, or just glitches in data? (SOHO via Horizons) (you can read more about it there):

If you look closely at the "top" there's a little blip, and excursion toward the sun. I think this is the famous, frightening episode in June to November 1998 when SOHO was almost lost. There is a page of recovery docs or you can read about it in Aerospace America May 1999: Saving SOHO or the article by ESA's F.C. Vandenbussche SOHO’s Recovery – An Unprecedented Success Story or for the more of the technical details, Roberts 2002 The SOHO Mission L1 Halo Orbit Recovery From the Attitude Control Anomalies of 1998.

## ISEE-3

In this case the spacecraft was not lost so much as people simply stopped talking to it/looking for it for a while:

From Wikipedia's International Cometary Explorer

ISEE-3 was the first spacecraft to be placed in a halo orbit at the L1 Earth-Sun Lagrangian point. Renamed ICE, it became the first spacecraft to visit a comet, passing through the plasma tail of comet Giacobini-Zinner within about 7,800 km (4,800 mi) of the nucleus on September 11, 1985.

NASA suspended routine contact with ISEE-3 in 1997, and made brief status checks in 1999 and 2008.

On May 29, 2014, two-way communication with the spacecraft was reestablished by the ISEE-3 Reboot Project, an unofficial group[6] with support from the Skycorp company. On July 2, 2014, they fired the thrusters for the first time since 1987. However, later firings of the thrusters failed, apparently due to a lack of nitrogen pressurant in the fuel tanks. The project team initiated an alternative plan to use the spacecraft to "collect scientific data and send it back to Earth", but on September 16, 2014, contact with the probe was lost.

## Voyager 2

The question Which Voyager spacecraft “mutinied”, and what really happened? describes a situation where the spacecraft was not really "lost" but it at least appeared that Voyager 2 was no longer taking commands.

• Wow, good answer. I think both of ours are complementary even if I got here 13 minutes later hahaha – Swike Sep 8 '19 at 13:50
• @Swike your answer is great! I'm enjoying looking through all those scenarios, thanks! – uhoh Sep 8 '19 at 20:46
• Great to see ISEE-3 here, that's the one I thought of – mikato Sep 9 '19 at 15:04

Not meeting the criteria of the question but there is day probe from Pioneer which was not intended to survive but continued to operate for 45 minutes after impact.

A number of other probes have lost contact for various software related reasons, including the voyagers but being software recovery is more possible than for a lander suffering some form of physical mishap.

Need to mention Akatsuki probe, which lost contact for an hour instead of 20 minutes entering Venus orbit in 2010. This incident led to five year delay in achieving destination.