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Astronauts bound for Mars should swing by Venus first, scientists say

An artist's depiction of a rocket carrying humans to Mars.
An artist's depiction of a rocket carrying humans to Mars.
(Image: © NASA/John Frassanito and Associates)

The roads of human spaceflight all seem to lead to Mars. For decades now, it's been the logical next step after the moon. 

But if you're an astronaut or a cosmonaut on your way to or from Mars, you might make a surprising pit stop along the way: Venus.

A flight to (or from) Mars can happen more quickly and cheaply if it "involves a Venus flyby on the way to or on the way home from Mars," Noam Izenberg, a planetary geologist at Johns Hopkins University, told Space.com.

Related: How will a human Mars base work? NASA's vision in images

Izenberg is one of a number of scientists and engineers advocating that a crewed mission to Mars also visit Venus. This group of researchers has drafted a white paper on the subject, to be submitted for peer review at Acta Astronautica. According to that paper, using Venus as a stepping stone to Mars isn't just one option — it's an essential part of a crewed Mars mission. 

"Venus is how you get to Mars," Kirby Runyon, a planetary geomorphologist at Johns Hopkins University who's on the white paper team, told Space.com.

To get between Earth and Mars, there are two options. The first, and simplest, is a conjunction mission, in which a spacecraft flies between the two planets when they align in their orbits. After reaching Mars, astronauts would need to wait for the planets to align again before they could return to Earth. That wait could take as long as a year and a half.

The second option is an opposition mission, in which — either en route to Mars or on a return trip — a spacecraft would slingshot past Venus, using the planet's gravity to alter course. Using Venus for such a gravity assist would dramatically reduce the amount of energy needed for the trip, saving on fuel and weight, and therefore also on cost. This is the type of mission that these researchers support. 

A cutaway diagram of an Apollo-inspired rocket that could fly humans past Venus. (Image credit: NASA)

"It's preferable to fly by Venus for a gravity assist on the way to Mars," Paul Byrne, a planetary geologist at North Carolina State University, also on the white paper team, told Space.com.

A conjunction mission might look simpler on paper, but the opportunities for such transfers are few and far between. Mars and Earth's orbits only align to allow for a conjunction mission every 26 months. In contrast, you could theoretically launch an opposition mission every 19 months.

Furthermore, opposition missions allow for much shorter stays at Mars: astronauts could even go for trips as short as one month — as opposed to the year and a half a conjunction mission might take. While the actual amount of time that this flight might take could be longer, adding Venus to a Mars flight plan means that astronauts could return to Earth as much as a year sooner. 

Additionally, in the event something were to go wrong during such a mission, going to Venus first also allows the possibility of quickly changing course and returning to Earth in a much shorter timeframe.

"You … greatly simplify the logistics of going to Mars, especially from the perspective of crew health," Runyon said.

But Izenberg and his colleagues aren't just treating Venus as a layover. They believe Venus would be a valuable destination

"There's science at two planets for much less than the price of two separate crewed missions," Byrne said.

Robotic probes have captured an incredible amount of data through observations at Venus, but scientists think that visiting Venus with a crewed mission opens up new possibilities — especially if those visitors bring probes or rovers with them. "What humans can do better than robots is respond to observations on the fly," Martha Gilmore, a planetary geologist at Wesleyan University, who isn't involved with the white paper group, told Space.com. 

A diagram showing the potential trajectory of a crewed Venus-flyby mission to Mars. (Image credit: Izenberg, et. al./(JHUAPL))

Astronauts at Venus wouldn't have to deal with the lag — which could be anywhere between five minutes and 28 minutes — thanks to the time light takes to travel between Earth and Venus. Therefore, according to Runyon, "the crew would be able to control rovers on the surface and aircraft in the atmosphere in real time with a virtual reality headset and a joystick."

"If you do that with a purely robotic mission from Earth," Izenberg added, "you can't really do that easily."

The white paper team believes that piloting drones during such a flyby is more than just a dream. Runyon said that, if you look between the lines, the evidence is there that NASA is planning for an opposition-type mission. This NASA report released in April mentions "two-year Mars class missions" as a future goal. 

"Assuming that this report is talking about normal forms of propulsion," said Runyon, "the only way you can get to Mars and back in two years is if you include a Venus flyby."

You can follow Rahul Rao on Twitter at @raorr108. Follow us on Twitter @Spacedotcom and on Facebook

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  • Andrew N
    Admin said:
    To get to Mars cheaper and faster to save time and open up new mission windows, scientists say there's an easy shortcut: fly by Venus on the way.

    Astronauts bound for Mars should swing by Venus first, scientists say : Read more

    Speed increase?
    Time savings?
    Extra braking requirements on reaching Mars?
    Reply
  • Matthew Bruder
    There is an interesting 1967 study which considered a fly-by of Venus with a continuation to Mars.
    Reply
  • Helio
    That's great news. It reminds me of the idea to build a tunnel from NYC to LA where the travel speeds in a vacuum tube on a magnetic rail produce a very short travel time just by using, primarily, gravity.
    Reply
  • egribble
    Admin said:
    To get to Mars cheaper and faster to save time and open up new mission windows, scientists say there's an easy shortcut: fly by Venus on the way.

    Astronauts bound for Mars should swing by Venus first, scientists say : Read more
    The primary reason for not taking this path is radiation. Solar radiation is a nightmare once you are beyond the Van Allen Belts. Taking people even closer to the sun is dangerous, there is only one realistic direction, outwards away from that nuclear furnace.
    Reply
  • Lovethrust
    egribble said:
    The primary reason for not taking this path is radiation. Solar radiation is a nightmare once you are beyond the Van Allen Belts. Taking people even closer to the sun is dangerous, there is only one realistic direction, outwards away from that nuclear furnace.
    The minor amount of extra solar radiation would be more than compensated for by shorter stays on Mars, notto mention the option of an abort to Earth not available for Mars direct.
    Reply
  • funkpoppy
    Gaetano Crocco proposed a Venus-boost-to-Mars mission in 1956. Someone is borrowing heavily and not giving credit where it is due.
    Reply
  • Helio
    Lovethrust said:
    The minor amount of extra solar radiation would be more than compensated for by shorter stays on Mars, notto mention the option of an abort to Earth not available for Mars direct.
    Yes, the shorter sailing time the less the risk of being caught in a storm (flares). The serious radiation events come from flares and CMEs. Spacecraft have safe areas that have extra shielding from such events, but the less time stuck in these areas the better.
    Reply
  • Helio
    funkpoppy said:
    Gaetano Crocco proposed a Venus-boost-to-Mars mission in 1956. Someone is borrowing heavily and not giving credit where it is due.
    That's not surprising, but I hope credit is given to those who demonstrated feasibility.
    Reply
  • Torbjorn Larsson
    The year long travel times suits slow crawl NASA, modern interplanetary travel technology not so much - you want to reach Mars within 3-6 months to minimize travel time and radiation dose.

    And on the balance, the white paper review covers decades of these types of deliberations.

    Lovethrust said:

    The minor amount of extra solar radiation would be more than compensated for by shorter stays on Mars, notto mention the option of an abort to Earth not available for Mars direct.

    That is the problem, since Starship proposes to start under ground colonization - rare returns.

    The abort option is limited - a Starship flotilla has continuous backups (and return from Mars) instead.

    funkpoppy said:

    Gaetano Crocco proposed a Venus-boost-to-Mars mission in 1956. Someone is borrowing heavily and not giving credit where it is due.

    It's a white paper review, so they mention early NASA reviews and you have to dig some more to see if Crocco is not covered.
    Reply
  • Helio
    I pulled out my copy of The Real Book About Space Travel, 1952, Hal Goodwin. He gives Von Braun's plan presented to the Second International Congress of Astronautics in London, 1951.

    Von Braun’s plan for travel to Mars:

    ♦ Huge "three step" ships would use over 500 million tons of fuel for 950 trips to a space platform.
    ♦ They would deliver 36,600 tons of fuel for the trip.
    ♦ 70 people would be in space.
    ♦ They would be supplied with several hundred tons of supplies and equipment.
    ♦ They would build 10 ships in space. The ships would probably not look like comic book ships but more like globe-type structures framed together.
    ♦ Braun called the ships “orbit to orbit ships" since they left Earth’s orbit and would remain in Mars' orbit serving as space stations, “perhaps next to Phobos.”
    ♦ Three large-winged ships would be used to land on Mars, carrying 50 astronauts to Mars surface.
    ♦ After about 400 days, two ships would return to the orbit-to-orbit ships.
    ♦ Total time would be 2 years, 239 days.
    ♦ The most dangerous part would be entering Earth’s atmosphere, where a series of “braking ellipses” would slow the ships and give them cooling time between each braking event.
    Reply