How long does it take to get to mars? A straight forward question might not have as straight forward of an answer. Typically, if you ask this question you will get an answer of about 7-8 months. But is that correct? The answer is sometimes, and maybe.
So, if we start with an expert on how long it takes to get to Mars and the types of things that impact a mission. Possibly one of the best-known expert organizations in the world is National Aeronautics and Space Administration or better known as NASA. NASA has had its fair share of robotic missions to Mars, some successful and others not so successful.
According to NASA, it depends on how you go. There are several things that impact the duration of the trip to Mars. A few factors include
1. What kind of rocket is used and what technologies are available?
2. Where the Earth is as compared to Mars.
3. How fast you go and how much fuel you want to use.
Actually, it isn’t about how many years will it take to get to Mars, but how many months. Over the last 50 years, a typical one-way trip to Mars takes less than a year using current chemical rocket technology. NASA robotic missions usually take about 8 months to travel to Mars but could be as little as 3 months even with the current technology. So, the time actually depends heavily on the timing of the mission and the relative position of Earth and Mars in their orbits. NASA wants to do better. Since 8 months is a long time, NASA is exploring other options that will minimize the duration of a human trip to Mars. Before we get into the details of the technology, we need to understand a little more about Orbital mechanics.
A one way transfer orbit between Earth and Mars. Credit: NASSA https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1969-030A
NASA typically uses Hohmann transfers as they are the most propellant-efficient means of moving between two circular orbits. (The approximation is that both Earth orbit & Mars orbit are roughly circular) Hohmann transfers require the smallest change in spacecraft velocity. Less velocity change translates into less fuel and mass required to be placed into orbit from Earth to accomplish the mission. To use a Hohmann orbit transfer, two propulsive maneuvers are required and are assumed to be instantiations – so that means that constant thrust space travel options like SEP use other transfer orbit calculations. The first thrust breaks the spacecraft free from Earth’s gravity (Earth orbit) and places it on a path to intersect the desired orbit, which in this case is Mars. The spacecraft is then said to be in the Hohmann transfer ellipse, which is an orbit tangent to both circular orbits. Aside from a mid-course correction (The spacecraft actually will need to account for variations in the transfer orbit), the spacecraft has “coasts” to the point that connects the Hohmann transfer orbit with Mars orbit. Once at Mars, the spacecraft fires its engine again, now to circularize its orbit, allowing it to enter the new orbit.
Upcoming transfer options from Earth to Mars. Data from: NASSA https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1969-030A
Here are some of the actual numbers for how long it took to Get to Mars:
Days Year Mission
228 1965 Mariner 4
155 1969 Mariner 6
128 1969 Mariner 7
168 1971 Mariner 9
304 1975 Viking 1
333 1975 Viking 2
308 1996 Mars Global Surveyor
212 1996 Mars Pathfinder
200 2001 Mars Odyssey
201 2003 Mars Express Orbiter
207 2003 Spirit
201 2003 Opportunity
210 2005 Mars Reconnaissance Orbiter
254 2011 Mars Science Laboratory
242 2018 InSight
307 2014 Mars Atmosphere and Volatile EvolutioN (MAVEN)
3 min Speed of light (transmissions to and from when close)
Mariner 6 & 7 visual Credit: NASSA
The Mariner spacecraft were all relatively small robotic explorers, each launched on an Atlas rocket. The timing of Mariner 6 and 7 allowed them to have a shorter flight duration based on the alignment of the Earth and Mars at the time. The dry weight of Mariner 6 and 7 were each less than half a ton, coming in at 413 kg (908 lb.) each (dry weight is excluding onboard rocket propellant).
Mariner 6 and 7, launched 2/24/69 and 3/27/69 and had Mars flybys 7/31/69 and 8/5/69; They collected data with the onboard equipment including wide- and narrow-angle cameras with a digital tape recorder, infrared spectrometer and radiometer, ultraviolet spectrometer, radio occultation, and celestial mechanics. Mariner 7 was launched on an Atlas SLV-3C/Centaur (AC19, spacecraft 69-4). It utilized a direct-ascent trajectory to Mars from Cape Kennedy Launch Complex 36A meaning that it did not orbit first, but rather launched directly and kept going. At the closest approach, 05:00:49 UT on 5 August, Mariner 7 was 3430 km above the Martian surface.
In celestial navigation, an ephemeris (plural: ephemerides) gives the trajectory of naturally occurring astronomical objects as well as artificial satellites. This provides the object’s position and velocity over time. The needs of the Mariner Mars 1969 mission necessitated the general improvement of planetary ephemerides. A new 60-year numerical computation of the planets of the solar system was made corrections obtained from a weighted least-squares fit available data set spanning the period 1910-1968.
Nuclear Deep Space Transport Concept Credit: NASA
https://www.nasa.gov/directorates/spacetech/game_changing_development/Nuclear_Thermal_Propulsion_Deep_Space_Exploration
You may have noticed that NASA said, using current technology. Over the past 50 years, technology to make us go faster to get to Mars really has not been the key focus of research. As can be seen, by the travel duration of the various spacecraft that have visited Mars, they all fall between 120 and 350 days.
The issue is that the faster you go, the more fuel you need to get going that fast. With chemical rockets, that mass adds up very quickly. So, what about other propulsion modes? We know that nuclear can be very dangerous but can also provide an efficient means of generating large amounts of energy. For spacecraft propulsion, nuclear-powered propulsion could be an option for some missions.
Nuke Mars??? Elon Musk didn’t mean this type of Nuke…
NTRs have been proposed as a spacecraft propulsion technology all the way back to the 1950s. The US developed NTR propulsion technology through 1973, but it was defunded to allow focus on Space Shuttle development. You can read more on the US nuclear-powered rocket program and concepts like the NERVA engine.
NTR propulsion would likely be useful for both the precursor and unmanned cargo missions since thermal nuclear rockets have a higher specific impulse (ISP) than chemical rockets making them far more efficient than chemical propulsion systems. To change the velocity of a spacecraft by a given amount takes less mass. Less fuel means a reduction in the total mission cost by reducing the need for material to be launched into space. Sounds great, so what is the catch? The US defunded the program in the 1970s. There have been several efforts to restart development, but the technology has not been sufficiently developed to make it viable for a manned mission. An NTR could be a viable option for propulsion to Mars for a manned mission as it would be high enough thrust but also reduce greatly the required fuel mass.
ElectricPropulsion Powered Deep Space Transport Credit: NASA
To further reduce the cost and risk of a human mission to Mars, NASA plans to send equipment and cargo in advance via unmanned cargo missions. Rather than using high thrust chemical engines, NASA would use a highly efficient electric propulsion (EP) system. These systems would not leverage the same type of orbit transfers as they lack the necessary thrust over a short time. Instead, the EP system would provide a high specific impulse (ISP) making them far more efficient than chemical propulsion systems, but a low thrust thus making a slow gradual spiral orbit change.
There is a tradeoff for EP. EP produces much lower thrust levels as compared to traditional chemical rockets. The transfer, therefore, takes longer to occur. For unmanned missions, this trade-off may be acceptable. For manned missions, the longer time in space may not be acceptable since the savings in fuel will likely be offset by increased consumption of food and water as well as increased exposure to dangerous cosmic radiation. Therefore there is less willingness to trade transfer time for efficiency for time for a human Mars mission. NASA awarded an $18.8 million contract to BWXT Nuclear Energy in 2017. BWXT is a company with a long history of making nuclear fuel for the U.S. Navy. Nuclear thermal propulsion can provide a substantial advantage over current chemical and electric propulsion systems through a reduction in travel duration to Mars by 20 or 25 percent.
Even though the EP produces much lower thrust levels, it can be highly effective in unmanned missions using current technology. Since the ISP is high, to change the velocity of a payload by a given amount takes a much smaller mass of fuel than it would of conventional chemical rocket fuel. The downside is that the transfer takes longer to occur. For unmanned missions, the extra time is less of a concern, therefore to trade transfer time for efficiency is desirable especially when you consider since this greatly reduces the mass of propellant that must be launched to low earth orbit (LEO). Less mass launched to LEO results in a lower total mission cost as the cost of launching material into orbit is still very high.
There are other differences between chemical and electric propulsion transfers. Chemical transfers involve a few short-duration engine firings, which provide the necessary change in spacecraft velocity. These “burns” provide a very quick addition of energy to the spacecraft resulting in a change in velocity. Following these “burns”, the spacecraft effectively “coasts” to its destination, so the engine is used only for a very short period of time. On the other hand, Electric propulsion systems involve continuous utilization of the engine. The resulting thrusting force provides a gradual addition of energy to the spacecraft’s orbit over a long duration. Payloads launched to LEO require a period of continuous EP thruster firing that creates the spiral trajectory of increasing orbital energy, slowly bringing the spacecraft to a high earth orbit (HEO) and eventually allowing it to escape the gravitational pull of Earth. At that certain point where the spacecraft velocity will increase to the point where it escapes earth orbit, it then enters into a heliocentric transfer orbit. (The pull of the Sun is now overcoming that of the Earth’s localized pull) The EP continues to provide thrust still slowly increasing the energy of this orbit as the spacecraft makes its way to Mars.
Look for the follow up article that starts going into more details next week.
About The Author
Bill D'Zio
Co-Founder at WestEastSpace.com
Bill founded WestEastSpace.com after returning to China in 2019 to be supportive of his wife's career. Moving to China meant leaving the US rocket/launch industry behind, as USA and China don't see eye to eye on cooperation in space. Bill has an engineering degree and is an experienced leader of international cross-functional teams with experience in evaluating, optimizing and awarding sub-contracts for complex systems. Bill has worked with ASME Components, Instrumentation and Controls (I&C) for use in launch vehicles, satellites, aerospace nuclear, and industrial applications.
Bill provides consulting services for engineering, supply chain, and project management.
0 Comments