# Hermes Mission: The Martian Flight Path

Chart the Hermes mission from The Martian across the inner solar system: the abort, Mark Watney's long wait on Mars, the Rich Purnell slingshot and the rescue, with mission days and sols counted together

By Ham Sandwich

Topic: Space

[Open the interactive Jig](https://ask.jig.com/j/M9Kxki7vJ54k)

## Guide

### 1. Hermes Mission

In The Martian, the spaceship Hermes carries six astronauts from Earth to Mars\. This map shows the inner solar system from above: the Sun, Earth's orbit in blue and Mars's orbit in red\. Drag to turn the map\. The counters at the top keep the mission clock\.

The planets are drawn hundreds of times bigger than they really are\. Switch on true size to see how empty space is\.

### 2. The long way out

Hermes leaves Earth on 7 July 2035 and spirals outward on gentle ion engines\. Watch the mission day counter: the trip takes about four months\. Mars is a moving target, so Hermes aims for where Mars will be, not where it is now\.

Hermes is drawn huge so you can follow it\. At true size it would be far smaller than a speck of dust on this map\.

### 3. Sol 6: the storm

A day on Mars is called a sol, about 24 hours and 40 minutes long\. On sol 6 a fierce dust storm forces the crew to leave\. Flying debris knocks Mark Watney out of sight, and his crewmates, sure he is gone, launch without him\. Hermes turns for home\.

The author admits the storm is the made\-up part: Martian air is so thin that even fast winds push very gently\.

### 4. Alone on Mars

Mark is alive, alone with the Hab, two rovers and food meant for a short stay\. Watch his sol counter climb while Hermes flies away\. The nearest people are now hundreds of millions of kilometres off, and even a radio message takes many minutes to reach him\.

Mark grows potatoes in Martian soil to stretch his food\. The bright blue star in his sky is Earth\.

### 5. Rich Purnell's idea

Hermes is nearly home, and a new rocket could not reach Mark before his food runs out\. Rich Purnell, an astrodynamics expert at NASA's Jet Propulsion Laboratory \(JPL\), finds another way: do not stop at Earth\. Fly past it, let Earth's gravity fling Hermes back out, and meet Mars again\. Compare the two plans\.

Going back adds 533 days to the crew's mission\. They all vote to go\.

### 6. Slingshot past Earth

Around day 364 Hermes swings close past Earth without stopping\. Earth's gravity bends its path and flings it onto a new loop, like a ball whipped around a tetherball pole\. On the way it catches a supply probe launched by China's space agency\.

This trick is called a gravity assist\. Real spacecraft such as Voyager and Cassini used it too\.

### 7. The long loop back

Now Hermes loops once around the Sun and climbs back out toward Mars, a journey of almost a year\. Meanwhile Mark drives his rover about 3,200 kilometres to the crater where his ride off Mars waits\. Watch both counters: days for the crew, sols for Mark\.

Mark spends 549 sols on Mars, about a year and a half on an Earth calendar\.

### 8. Rendezvous at sol 549

Hermes cannot stop at Mars: it races past at about 5\.8 kilometres every second\. Mark must climb into space to meet it, in a stripped\-down rocket called the MAV, the Mars Ascent Vehicle\. Launch it and watch the two paths meet\.

Commander Lewis, tethered to Hermes, catches Mark at the meeting point\.

### 9. Home at last

With Mark aboard, Hermes reaches Earth on 21 December 2037, day 898 of a mission planned for 396 days\. Follow the whole orange path: out to Mars, home toward Earth, the slingshot, a loop round the Sun, the rescue and the last trip home\.

For more than 18 months, Mark was the only person on an entire planet\.