How Long Does it Take to Get to The Sun?

Important Factors

There are typically four factors when considering a more precise flight duration to any astronomical object:

• Whether or not the spacecraft is sent to other celestial objects either for scientific studies and/or gravity assist using a slingshot flight maneuver. While a quick flyby mainly for a gravity assist will dramatically increase speed and decrease travel time, time spent studying that planetary system becomes a little more complicated in terms of its actual impact on average velocity and travel time.
• The launch vehicle capabilities as much of the speed of the aircraft (disregarding gravity assists and thruster adjustments) will be determined by the speed the rocket can attain after escaping Earth’s gravity, which requires a minimum of 7 miles/ 11.2 kilometers per second (25,000 mph or just over 40,000 km/ hr) just to reach Earth’s escape velocity. As a baseline, the Apollo spacecraft reached a speed of 8 km/sec.
• Slowing down requires time by either reverse-firing thrusters in space or utilizing atmospheric re-entry if landing. A flyby will be shorter than an orbit insertion (which is the best we can do for the Sun and many other destinations like our gas giants) or landing on the surface of an object like a moon. Even more so than other destinations, a significant amount of effort, time, and fuel is spent on NOT being sucked into the Sun (unless that is the goal). The Sun is the biggest thing around, holding everything in the Solar System in place. Its gravitational pull is massive.
• An astronomical destination is not a fixed point in space like a house since it is constantly moving. Planets and other objects in the solar system move around the Sun and the Sun moves around the galaxy (we are never truly still). So, we can’t only plan to reach the end destination based on the distance when we launch, but where it will be by the time we reach it. This calculation also has to be done for any gravity assists that will be planned along the trip.

While theoretical flight plans are helpful, what real flight plans can we compare to better understand more realistic travel times to the Sun?

Past missions to the Sun

Many of the spacecraft that study the Sun do not go to the Sun. For example, while the Solar and Heliospheric Observatory (SOHO) is the longest-running solar observatory to date, it sits at LaGrange Point 1, not even halfway to the Sun from Earth as it provides an uninterrupted view of the Sun. 

However, we have sent five missions to the Sun.

Helios

Helios-A and Helios-B (renamed Helios 1 and Helios 2 after launch) were a pair of probes launched into orbit around the Sun to study our star. It was a joint venture between German Aerospace Center (DLR) and NASA. The project set a maximum speed record for spacecraft of 157,078 mph (252,792 km/h or 70,220 m/s). 

Helios-A was launched on the first operational flight of the Titan IIIE rocket and the same procedure was used for Helios-B. There were several instrumental issues for Helios-A so multiple adjustments were made to Helios-B to address these concerns. Today they are no longer functional, but remain in orbit around the Sun. Below are key mission events:

Helios-A took less than three months from launch to the first perihelion while Helios-B took just about three months. Neither used flybys.

Ulysses

Ulysses was a joint ESA-NASA mission designed to study and explore the solar poles in three dimensions. The mission originally planned to utilize two spacecraft, one from ESA and one from NASA, each of which would have flown over opposite poles and was dubbed the International Solar Polar Mission (ISPM). However, NASA canceled its spacecraft and instead focused on providing instruments, the launch vehicle, and communications and tracking. 

Ulysses completed nearly three complete orbits of the Sun during more than 18 years in service and was the first mission to survey the space environment above and below the poles of our Sun. The 818-pound (371-kilogram) Ulysses spacecraft launched from the Space Shuttle Discovery.

From launch in October 1990 to the beginning of observations in June 1994, Ulysses took 3 years and 8 months, though many count it reaching the region of space around it a year earlier. 

It’s also important to remember its closest approach was in March 1995 so we have to consider what qualifies as “arriving at the Sun”. Ulysses first did a gravity assist at Jupiter, accounting for the extended time period.

Parker Solar Probe

Often known as the mission to “touch the Sun”, Parker Solar Probe is focused on revolutionizing our understanding of our star over the course of 24 orbits around the Sun. The Solar Probe Plus Spacecraft at 1,510 pounds (685 kilograms) at launch sat on top of a Delta IV-Heavy with Upper Stage launch vehicle. 

The mission’s route will utilize seven Venus flybys over nearly seven years to gradually shrink its orbit around the Sun. Check out this animation of the Parker Solar Probe’s orbits around the Sun. 

Below are key dates in the mission, separated by year for easier reading. Note that perihelion means the point in an orbit that is closest to the Sun (think “peri” like perimeter or perilous or p for proximity) while aphelion is the point in an orbit that is furthest away.

In August 2023, Parker’s current speed is about 32,508 mph (52,315 kph) and since it is currently heading toward Venus for its sixth flyby, its current distance from the Sun is quite far: at over 69,191,441 miles (111,352,830 km).

At its closest approach in 2025, it will come as close as 3.83 million miles (6.16 million kilometers) to the Sun, a tenth of the orbit of Mercury, (on average, about 36 million miles from the Sun), and about seven times closer than the current record holder (the Helios 2 spacecraft, which came within 27 million miles in 1976). 

At this point, it will zip around the Sun at approximately 430,000 mph (700,000 kph), fast enough to travel from Philadelphia to Washington, D.C., in one second. Its orbit will be 88 days. 8.92 miles per second (14.35 km/s) 

The first perihelion was achieved only three months after launch, even including a Venus flyby in contrast to the Helios crafts.

Solar Orbiter

Solar Orbiter is a joint ESA and NASA mission delving into the conundrum of how the Sun creates and controls the ever-changing space environment throughout our solar system by studying the heliosphere, the bubble of charged particles and magnetic fields blown out to over twice the distance to Pluto. 

Over the course of 22 orbits around the Sun, it is traveling as close as 26 million miles (42 million km) from the Sun to study the magnetic fields, waves, energetic particles, and plasma escaping the Sun. It launched on a United Launch Alliance Atlas V 411 rocket, utilized multiple gravity assists from Earth and Venus, and then about 3.5 years later entered an elliptical orbit around the Sun, completing one revolution every 168 days. 

It is using gravity assists from Venus and Earth to gradually lift itself out of the ecliptic plane that all the planets lie in up to an angle of about 24 degrees above the solar equator (33 degrees if the extended mission is approved) to capture the first images of the poles from high latitudes. It can hover over specific spots when it almost matches the Sun’s rate of rotation at its fastest speed. 

Together with Parker Solar Probe, they are providing never before seen data to help us better understand our star.

From launch to first perihelion, Solar Orbiter took 4 months to arrive at the Sun.

General Estimate for Probes

As we have seen, you can reach 1st perihelion in orbit in 3 months, even with a Venus flyby. Subsequent gravity assists over months and even years are typically used to get closer and closer without getting sucked into the star. 

Theoretical Estimates

What about humans traveling to the Sun? It’s important to note that currently there is no safe way to send a crewed mission to the Sun or even Mercury. The temperatures and radiation threats are too high. In completely theoretical terms, the fastest that humans have ever traveled in space is 24,791 mph (39,897 km/ hr), which was achieved by the returning Apollo 10 astronauts in May 1969. At that speed, we could theoretically reach the Sun in about 155 days or about five months, but that wouldn’t include the time needed to slow down. 

In terms of light speed, light from the sun takes about 8 minutes and twenty seconds to reach the Earth, so if in the future we could travel at the speed of light, which the current understanding of physics says is an impossibility for anything besides light, it would take less than 8 and a half minutes. 

Conclusion

The Sun sits about 92,955,807 miles (149,597,870 kilometers) away. The calculation for how long it would take to get there is highly dependent on the speed achieved, the route, the number of “stops”, the number of gravity assists, and the approach procedure in which we slow down. Do we go straight to the Sun or utilize gravity-assist maneuvers from other planets, especially to save on fuel?

Based on past and current missions to our star, it takes probes about 3-4 months to “arrive” at a first perihelion in orbit. However, subsequent gravity assists are often utilized to get us closer and closer. It is important to remember that crewed missions to the Sun are not considered viable due to radiation concerns (even Mercury is a no-go for humans), but who knows what innovations the future may hold? Perhaps someday in the future, we can protect astronauts in a spacecraft enough to have them visit inside Mercury’s orbit or even closer to the Sun.