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SPACE.com Columnist Leonard David

Interstellar probe: Has its time finally come?

An adult and a child are silhouetted against a solar system map.
The Interstellar Probe, a mission to provide a unified view of our heliosphere, out into nearby interstellar space. (Image credit: Johns Hopkins/APL)

There is promising new work underway to pursue a deep space robotic interstellar mission. 

Called Interstellar Probe, this venture could capture a unified view of our heliosphere, out into nearby interstellar space. All of that sounds exceedingly lofty, ambitious, and tough-to-do.

But there's no need to wait for new technology, say advocates — it's here, and one booster of choice for the mission could be NASA's Space Launch System (SLS).

Related: A Wild 'Interstellar Probe' Mission Idea Is Gaining Momentum

Long overdue

"It isn't about where we are going. It's about the journey out there. And it is a journey now long overdue," believes physicist Ralph McNutt Jr. at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

As now visualized in a recent study, Interstellar Probe would utilize today's technology to take the first explicit step on the path of interstellar exploration, and can pave the way, scientifically, technically, and programmatically for more ambitious future journeys — and to conquer more go-getting science goals.

Furthermore, with the new class of super heavy-lift launch vehicles in the works — notably NASA's SLS — a scientifically compelling Interstellar Probe mission can now become a reality.

"Our team put a lot of work into making sure the study was as thorough and detailed as possible, while also casting a 'wide net' of possibilities. We eagerly look forward to what our colleagues with the Solar and Space Physics Decadal Survey have to say," McNutt said. 

Relay race

Interstellar Probe is a decades-long mission to reach several hundreds of astronomical units (AU) away from Earth while providing new unified, measurements of the conditions throughout the heliosphere and through the heliosheath — the outer shell of the bubble of charged particles around our Sun.

By moving forward on Interstellar Probe, it will take up the relay race that began with Pioneer 10, followed by Voyager 1 and Voyager 2.

We already have the technology to travel as far and as fast as possible: The Space Launch System Block 2 cargo version could be used to carry the spacecraft as well as a 3rd and 4th stage rocket boosters. Solar system escape speeds of at least twice that of Voyager 1 — up to 7.2 astronomical units per year — should be doable using this system.

Hurling a probe outward on such an adventure has been under discussion for almost half a century, McNutt said. With the 40-year-old Voyagers closing out their operational lifetimes as their power supplies continue to dwindle, further progress requires a new initiative, he said.

The latest design of a proposed Interstellar Probe spacecraft, which would be outward bound for new discoveries. The goal is to reach the pristine local interstellar medium, nearly 400 astronomical units (AU) away, at about 7.2 AU per year.

The latest design of a proposed Interstellar Probe spacecraft, which would be outward bound for new discoveries. The goal is to reach the pristine local interstellar medium, nearly 400 astronomical units (AU) away, at about 7.2 AU per year. (Image credit: Johns Hopkins APL/Steve Gribben)

Furthest presence

"We, the human race, have been reaching farther and farther from the Sun since the launch of Pioneer 10 in 1972. Since then, there has always been a 'furthest presence' moving outwards in the solar system and to regions beyond," McNutt told Space.com.

Sometime within the next decade, the Voyagers will fall silent. That is a matter of physics, engineering and "the cold equations," McNutt added. 

"So the question is: Will that also herald a retreat from pushing the bounds of knowledge, or at least a handover of the baton to a different player on this planet? We make the history of future generations," said McNutt, "and we do that by our actions every day that we live. So who are we to deprive subsequent generations of the next step to the stars? Why now? Rather: Why not now?"

An illustration of the Pioneer 10 probe.

An illustration of the Pioneer 10 probe. (Image credit: NASA)

Vantage point

"I think Interstellar Probe is an outstanding concept, said Paul Gilster, the creative drive behind the website Centauri Dreams (opens in new tab) - Imagining and Planning Interstellar Exploration. It's a mission that could take us to 1000 AU in 50 years, he said, and give us a vantage point from which to see the heliosphere from the outside. 

"In that sense, it is both a heliophysics mission as well as a deep space mission with implications for future exploration. Learning more about the heliosphere, in turn, tells us more about the solar wind, a possible propulsion source for future sailcraft, and its interactions with interstellar conditions," Gilster told Space.com.

Interstellar Probe needs to be seen in context, Gilster said. 

Presently, there are the two NASA Voyager spacecraft, and at some point they will be joined by NASA's New Horizons probe. 

But neither of these missions nor the earlier NASA Pioneer spacecraft were built to study space outside our solar system, the region known as the Local Interstellar Medium. "Interstellar Probe would be the first mission whose instrumentation is expressly designed with this task in mind," said Gilster.

Interstellar Probe is a decades-long mission to reach several hundreds of astronomical units.

Interstellar Probe is a decades-long mission to reach several hundreds of astronomical units.  (Image credit: Johns Hopkins/APL)

Voyager plus?

Gilster said he often hears objections when he talks about Interstellar Probe: Is this just "Voyager Plus?" And who wants to wait 50 years for data? But these are mistaken assumptions, he said. 

Interstellar Probe is an entirely new class of mission designed to operate well beyond the Kuiper Belt. The 50 year period is a target for 1000 AU and based on optimistic ideas about how to find the necessary "delta-V" - the amount of "effort" that is required to change from one trajectory to another by making an orbital maneuver.

"But the point is that Interstellar Probe will do science the whole way," Gilster said. "We will be learning a great deal more than the Voyagers could tell us every year that this mission flies, not only about the interstellar medium but also about long-life electronics, deep space communications and the nature of our Sun's travel through the galaxy with its protective heliosphere. We'll also have plentiful targets for study as Interstellar Probe moves through the outer solar system and its abundant Kuiper Belt Objects."

Deep space precursor

Gilster envisions Interstellar Probe as a precursor to deeper space still, for humankind will eventually want to use technologies of the future to push into the Oort Cloud of comets to explore this vast, largely unknown region. 

"I think it is entirely fitting that Voyager veteran Ralph McNutt, who has done so much for our species' exploration of the solar system, should be principal investigator on the first probe designed to leave that system," Gilster said. "I wish he and his team at APL good fortune as they navigate the approval process that must follow."

For a detailed look at how this mission could be carried out, read the team's publication "Interstellar probe — Destination: Universe (opens in new tab)!" in the journal Acta Astronautica. 

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Leonard David
Leonard David

Leonard David is an award-winning space journalist who has been reporting on space activities for more than 50 years. Currently writing as Space.com's Space Insider Columnist among his other projects, Leonard has authored numerous books on space exploration, Mars missions and more, with his latest being "Moon Rush: The New Space Race" published in 2019 by National Geographic. He also wrote "Mars: Our Future on the Red Planet" released in 2016 by National Geographic. Leonard  has served as a correspondent for SpaceNews, Scientific American and Aerospace America for the AIAA. He was received many awards, including the first Ordway Award for Sustained Excellence in Spaceflight History in 2015 at the AAS Wernher von Braun Memorial Symposium. You can find out Leonard's latest project at his website and on Twitter.