Category Archives: Space Travel

How long does it take to get to each of the planets?

It is almost impossible to find an accurate illustration of the scale of the solar system because nearly all fail to treat the orbit spacings correctly. A clever approach is to create scaled models that span entire cities and place markers in public places for each of the planets. An example of this is the NASA/JPL Scale Model shown here. Once you understand the distances involved, the magnitude of the challenge is made much clearer.

In my book ‘Interplanetary Travel: An Astronomer’s guide‘ I discuss current and planned technologies for interplanetary travel. The bottom line is that it depends a lot on the particular trajectory that you take. Usually, the trajectories are in the form of a ‘great arc’ that gracefully connects a launch time at Earth with a destination point. These arcs are usually many times longer that the straight-line distance between the two planets at a particular moment in time. For reduced-cost travel, astrodynamicists often rely on gravity assists ‘Slingshot Orbits’ from the inner planets to reach Jupiter, and by Jupiter to reach more distant worlds. These loop-de-loops add years of extra travel time to a mission. Let’s assume for our calculations that we just take the simplest direct approach and use the minimum ‘opposition’ distance between Earth and a planet.

The table below gives you some sense for how long it takes to get to each planet at different speeds.

The Space Shuttle, of course, can’t leave Earth orbit but its speed is typical of manned spacecraft. The Galileo spacecraft, which explored Jupiter traveled twice as fast. These travel times are based upon using a big chemical rocket on Earth to blast the spacecraft into the right trajectory. But there is another technology that has been used for several decades.

Ion rocket motors get their speed by being constantly accelerated 24-hours a day for many months, and two versions of this technology are given for a low-power and high-power ion engine. Ssatellites orbiting earth often use ion engine technology for station-keeping. NASA has also used ion engine technology on two interplanetary spacecraft: Deep Space 1 and Dawn. Both spacecraft used very low thrust engines operating for thousands of days to get the spacecraft to asteroids (Dawn visited Ceres and Vesta; DS1: 9969 Braille) and comets (Borrelly) for study.

Finally, and at least on paper, solar sails can reach speeds of nearly that of the solar wind (500 km/sec),. Engineers are even now beginning to space-test this technology.

As you can see from the table, we are currently stuck in the mode of travel where it takes nearly 10 years to get to Pluto. Perhaps in another hundred years, this travel time will be reduced to a year or less… assuming Humanity feels a compelling economic need to continue this kind of exploration.

Method=ShuttleGalileoIon AIon BSolar Sail
Speed =28,000mph54,000mph65,000mph650,000mph200,000mph
Mercury52d27d22d2.2d7.3d
Venus100d52d43d4.3d14d
Mars210d109d90d9d29d
Jupiter1.9yr1yr303d31d100d
Saturn3.6yr1.8yr1.5yr55d179d
Uranus7.3yr3.8yr3.1yr113d1yr
Neptune11.4yr5.9yr4.9yr179d1.6yr
Pluto15.1yr7.8yr6.5yr238d2.1yr

Assumptions: Ion Drive using a constant thrust of A) 0.1 pounds B) 1 pound with turnaround deceleration added. Two years acceleration to reach top speed. Solar Sail estimated speed 450 km/sec or one million mph)

Another way to gauge the maximum speed of a spacecraft is by the exhaust speed of its engines. Engine exhaust speed is related to an engineering parameter called the Specific Impulse. SI is the exhaust speed divided by the acceleration of gravity at Earth’s surface. For example, chemical rockets have SI=250 seconds and so their maximum exhaust speeds are 250 x 9.8 m/sec2 = 2.4 km/sec. SInce no rocket payload can travel faster than its exhaust speed, we can compare planetary transit times in terms of the SI of the rocket technology.

In this table, I assume that the rocket continuously accelerates from Earth until it reaches half its destination distance, then turns around and decelerates for the second half of the trip. The relevant equations are

        distance = 1/2 acceleration x Time ^2
        speed = acceleration x time

With: distance in meters, time in seconds, speed in m/sec and acceleration in meters/sec^2

Destinationa=0.05a=0.15a=0.2
PlanetTime-ATime-BTime-CMax-SI
DaysDaysDaysSeconds
Mars2414834000
Jupiter804625110000
Saturn1136636160000
Uranus1669653230000
Neptune21412468300000
Pluto21412468300000

So if we could design a ship, call it System A, that produced a constant acceleration of a = 0.05 meters/sec^2, we could get to Mars in just 24 days. Similarly for System C with an acceleration of 0.2 meters/sec^2 the Mars trip takes only a week! For engineers,we can also estimate for System C that the Mars configuration would need SI=34,000 seconds to get us there in 8 days. If we wanted to get to Pluto with the same acceleration, it turns out that accelerating for half the 68-day trip would get you to a maximum speed of about 2900 km/sec which sets the limit to our exhaust speed and leads to a maximum SI of about 300,000 seconds! These SI estimates are far larger than the chemical rockets provide of 300 seconds, and so we have to look to entirely different technologies to make these travel times possible.

Sadly, it doesn’t matter if we drag along huge fuel tanks to run our chemical rockets. They will never provide the high exhaust speeds we need to carry both our fuel and payload to our destinations. We have to use technologies that enormously increase the exhaust speeds themselves.

What material is used to make spacecraft?


So far as an astronomer understands the ‘witchcraft’ of spacecraft design, very light weight and durable alloys of titanium, aluminum and magnesium are commonly used. This picture of the ISS shows many different materials that have to be made space-worthy to survive the extreme conditions of temperature and pressure. (Credit: NASA: STS-132).

Aluminum – Most commonly used conventional material (used for hydrazine and nitrous oxide propellant tanks). Low density, good specific strength. Weldable, easily workable (can be extruded, cast, machined etc). Cheap and widely available. Doesn’t have a high absolute strength and has a low melting point (933 K).

Magnesium – Higher stiffness, good specific strength. Less workable than aluminium. Is chemically active and requires a surface coating (thus making is more expensive to produce).

Titanium – Melting point 1933 F. Light weight with high specific strength. Stiff than aluminium (but not as stiff as steel) Corrosion resistant. High temperature capability. Are more brittle (less ductile) than aluminium/steel. Lower availability, less workable than aluminium (6 times more expensive than stainless steel). Used for pressure tanks, fuels tanks, high speed vehicle skins.

Ferrous Alloys like Stainless Steel – Have high strength. High rigidity and hardness Corrosion resistant. High temperature resistance (1200K). Cheap Many applications in spacecraft despite high density (screws, bolts are all mostly steel).

Austentic Steels – Non-magnetic. No brittle transition temperature. Weldable, easily machined. Cheap and widely available. Susceptible to hydrogen embrittlement (hydrogen adsorbed into the lattice make the alloy brittle). Used in propulsion and cryogenic systems.

Beryllium – Stiffest naturally occurring material (beryllium metal doesn’t occur naturally but its compounds do). Low density, high specific strength High temperature tolerance Expensive and difficult to work Toxic (corrosive to tissue and carcinogenic) Low atomic number and transparent to X-rays Pure metal has been used to make rocket nozzles.

Inconel’ (An alloy of Ni and Co) – High temperature applications such as heat shields and rocket nozzles. High density (>steel, 8200 km m-3).

Aluminium-lithium – Similar strength to aluminium but several percent lighter.

Titanium-aluminide – Brittle, but lightweight and high temperature resistant.

In the near future we may use combinations of plastics and various hybrid materials such as metal-matrix composites that will greatly reduce the weight of a spacecraft, and greatly reduce launch costs. In fact, carbon fiber technology has already been used to replace many spacecraft components, except for the outer spacecraft bulkhead itself. Bulkheads are still made from titanium, aluminum or other conventional metals and alloys because of the tremendous thermal and pressure demands. The B-2 Stealth Bomber used carbon fiber materials in its wings, but the forces it would be required to take and the thermal loading are quite small compared to a spacecraft launched from the ground, or re-entering the atmosphere from space.

Fiber-reinforced materials such as carbon, aramid and glass composites have the highest strength and stiffness-to-weight ratios among engineering materials. For demanding applications such as spacecraft, aerospace and high-speed machinery, such properties make for a very efficient and high-performance system. Carbon fiber composites, for example, are five times stiffer than steel for the same weight allowing for much lighter structures for the same level of performance. In addition, carbon and aramid composites have close to zero coefficients of thermal expansion, making them essential in the design of ultra-precise optical benches and dimensionally stable antennas. Some carbon fibers have the highest thermal conductivities among all materials allowing them to be incorporated as heat dissipating elements in electronic and spacecraft applications.

Even carbon nanotubes and fibers are being developed with spacecraft and rocket technology in mind. So, we have a lot to look forward to in this exciting arena. Every pound saved is a major reduction in launch cost to the tune of $5000 per pound. This means that if you replace a pound of aluminum with a pound of some exotic new alloy, you have almost $5000 per pound in new allow cost to play with because aluminum counts for only one percent of the $5000!

How long would it take to get to the nearest star?

In my book ‘Interstellar Travel:An astronomer’s guide‘ I discuss some of the modern and planned developments in fast space travel. For the most part, it’s all about speed!

Using the kinds of chemical-based propulsion systems we have today, and taking advantage of a ‘gravitational slingshot’ from Jupiter, we could probably get up to 150,000 miles per hour. The Galileo probe managed to get to about 106,000 miles per hour (18 km/sec) and currently holds the record for the fastest speed ever achieved by an artificial body. Alpha Centauri is about 4.3 light years from Earth or 40 trillion kilometers. At this speed it would take 72,000 years to get there, not including slowing down to enter the system.

Rocket designers have been studying ion propulsion since the 1950s, and mention of the technology often turns up in works of science fiction. Ion propulsion was featured in a September 1968 episode of Star Trek called “Spock’s Brain,” in which invaders steal Spock’s brain and flee in an ion-powered spacecraft. The same technology is used intermittently for altitude control aboard 11 Hughes-built communications satellites in geosynchronous orbit 22,300 miles (35,885 kilometers) above Earth. The above photo shows the NASA NEXT ion engine firing at peak power during 2009 testing at NASA’s Glenn Research Center(Image: NASA).

Deep Space 1 launched in 1998, was the first spacecraft to use ions as a primary means of propulsion. Instead of the fiery thrust produced by typical rockets, an ion engine emits only an eerie blue glow as electrically charged atoms of xenon are pushed out of the engine. Xenon is the same gas found in photo flash bulbs and lighthouse search lamps. Acceleration with patience In the engine, each xenon atom is stripped of an electron, leaving an electrically charged particle called an ion. Those ions are then jolted by electricity that is produced by the probe’s solar panels and accelerated at high speeds as they shoot out from the engine. That produces thrust for the probe. The ions travel out into space at 68,000 miles (109,430 kilometers) per hour. But Deep Space 1 doesn’t move that fast in the other direction because it is much heavier than the ions. Its cruising speed is closer to 33,000 miles (53,100 kilometers) per hour.

The thrust itself is amazingly light — about the force felt by a sheet of paper on the palm of your hand. It takes four days to go from zero to 60 (miles per hour). But once ion propulsion gets going, nothing compares to its acceleration. Over the long haul, it can deliver 10 times as much thrust-per-pound of fuel as more traditional rockets. Each day the thrust adds 15 to 20 miles (25 to 32 kilometers) per hour to the spacecraft’s speed. By the end of Deep Space 1’s mission, the ion engine will have changed its speed by 6,800 miles (11,000 kilometers) per hour.

Using current ion drive technology, with 10 times DS-1s acceleration of 25 km/hr per day, you could reach 1/2 the speed of light (540 million km/hr) in about 4900 years. For our journey to Alpha Centauri, you would accelerate for half the trip, turn around and decelerate for the second half. A bit of math shows what you get for travel time:

Distance to turn around = 2.1 light years or 20 trillion km 10x DHS acceleration is 250 km/hr/day or 8×10-7 km/sec/sec. At this acceleration, distance = 1/2 acceleration x Time2 so T = 228 years. You then turn the ship around and decelerate for another 228 years for a total trip time of 456 years! What is interesting is that this same ion rocket technology will let us travel to Mars in 270 days, so this isn’t really pushing the technology envelope very hard! If we could get to Mars in 30 days, then the same technology would get us to Alpha Centauri in about 50 years or a single human lifetime!

If you wanted to make the trip to Alpha Centauri in, say, 30 years, you would reach the half-way distance of 2.1 light years in 15 years. An acceleration rate, A, of 17 kms/sec per day would be needed. This is about 1000 times faster than Deep Space 1. At this pace, you would be traveling as fast as the solar wind (500 km/sec) in about one month, and would pass the orbit of Pluto in 100 days traveling at a speed of 1700 km/sec.

Nuclear rocket technology can make the trip even faster because the exhaust speeds can approach 20% the speed of light or higher. At these speeds, a trip to Alpha Centauri would take less than 25 years!

At what speed does the interstellar medium become lethal to high speed flight?


The dilute interstellar medium permeates space at a density of about one hydrogen atom per cubic centimeter. This image shows an all-sky map of this hydrogen observed by the Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey (Haffner, L. M. et al, 2003, Astrophysical Journal Supplement, 149, 405).. The Wisconsin H-Alpha Mapper is funded by the (US) National Science Foundation.

We do not really know what the interstellar medium looks like at the human-scale. If it is just stray hydrogen atoms you will just experience a head-on flow of ‘cosmic rays’ that will collide with your spacecraft and probably generate secondary radiation in the skin of your ship. This can be annoying, but it can be shielded so long as the particles are not ultra-relativistic. At spacecraft speeds of 50-90% the speed of light, these particles are not likely to be a real problem. At speeds just below the speed of light, the particles are ultra-relativistic and would generate a very large x-ray and gamma-ray background in the skin of your ship.

As it turns out, our solar system is inside a region called the Local Bubble where the density of hydrogen atoms is about 100 times lower that in the general interstellar medium. This Bubble, produced by an ancient supernova, extends about 300 light years from the Sun but has an irregular shape. There are thousands of stars within this region which is enough to keep us very busy exploring safely. Here is one version of this region by astronomers at the Harvard-Smithsonian Center for Astrophysics.

Interstellar space also contains a few microscopic dust grains (micron-sized is common) in a region about a few meters on a side. At their expected densities you are probably in for a rough ride, but it really depends on your speed. The space shuttle, encountering flecks of paint traveling at 28,000 mph (about 6 miles/second or 0.005 percent the speed of light) is pitted and pierced by these fast moving particles, but dust grains have masses a thousand times smaller than the smallest paint fleck, so at 0.005 percent light speed, they will not be a problem.

At 50 percent the speed of light which is the minimum for interstellar travel you will cover enough distance in a short amount of time, that your likelihood of encountering a large interstellar dust grain becomes significant. Only one such impact would be enough to cause severe spacecraft damage given the kinetic energy involved.

A large dust grain might have a mass of a few milligrams. Traveling at 50% the speed of light, its kinetic energy is given non-relativistically by 1/2 mv^2 so E = .5 (0.001 grams) x (0.5 x 3 x 10^10 cm/sec) = 1.1 x 10^17 ergs. This, equals the kinetic energy of a 10 gram bullet traveling at a speed of 1500 kilometers per second, or the energy of a 100 pound person traveling at 13 miles per second! The point is that at these speeds, even a dust grain would explode like a pinpoint bomb, forming an intense fireball that would melt through the skin like a hot poker melts a block of cheese.

The dust grains at interstellar speeds become lethal interstellar ‘BB shots’ pummeling your spacecraft like rain. They puncture your ship, exploding in a brief fireball at the instant of contact.

Your likelihood of encountering a deadly dust grain is simply dependent on the volume of space your spacecraft sweeps out. The speed at which you do this only determines how often you will encounter the dust grain in your journey. At 10,000 times the space shuttle’s speed, the collision vaporizes the particles and a fair depth of the spacecraft bulkhead along the path of travel.

But the situation could well be worse than this if the interstellar medium contains lots of ice globules from ancient comets and other things we cannot begin to detect in interstellar space. These impacts even at 0.1c would be fatal…we just don’t know what the ‘size spectrum’ of matter is between interstellar ‘micron-sized’ dust grains, and small stars, in interstellar space.

My gut feeling is that interstellar space is rather filthy, and this would make interstellar, relativistic travel, not only technically difficult but impossible to boot! Safe speeds for current technology would be only slightly higher than space shuttle speeds especially if interstellar space contains chunks of comet ice.

This is an issue that no one in the science fiction world has even bothered to explore! The only possible exception is in Star Trek where the Enterprise is equipped with a forward-directed ‘Brussard Deflector’ (that big blue dish just below the main saucer) which is supposed to sweep away particles before they arrive at the ship. This is very dubious technology because hydrogen atoms are not the main problems a ship like that would have to worry about, especially traveling inside a planetary system at sub-light speeds. It’s dust grains!

What happens when a human is exposed to a vacuum?


According to popular science fiction accounts, on a space station orbiting Saturn, a man inside a punctured spacesuit swells to monstrous proportions and explodes. On Mars, the eyes of a man exposed to the near-vacuum of the martian atmosphere, pop out of his head and dangle by their optic nerves on the sides of his face. En route to Jupiter on the Discovery spacecraft, Astronaut Dave Bowman space walks for 15 seconds with no helmet, and in no apparent pain, succeeds in reentering the Discovery through an open hatch. Fortunately, only in science fiction stories do humans ever come into direct contact with the vacuum of space, but these contacts are often portrayed as having horrific consequences.

To experience the vacuum is to die, but not quite in the gristly manner portrayed in the popular movies Total Recall and Outland. The truth of the matter seems to be closer to what Stanley Kubrik had in mind in 2001: A Space Odyssey.

According to the McGraw/Hill Encyclopedia of Space, when animals are subjected to explosive decompression to a vacuum-like state, they do not suddenly balloon-up or have their eyes pop out of their heads. It is, in fact, virtually impossible to compress or expand organic tissues in this way.

Instead, death arises from the response of the free gasses trapped within the tissues. When the ambient pressure falls below 47 millimeters of mercury, about 1/20 the atmospheric pressure at sea level, the water inside all tissues passes into a vapor state beginning at the skin surface. This causes the collapse of surface cells and the loss of huge amounts of body heat via evaporation. After 15 seconds, mental confusion sets-in, and after 20 seconds you become unconscious. You can survive this for about 80 seconds if a pressure higher than about 47 millimeters of mercury is then reestablished.

There have been instances of accidental exposure to a hard vacuum during space suit tests in vacuum chambers, and by pilots flying military aircraft at 100,000 feet. The experience was not fatal, or even exceptionally uncomfortable, for the typically 10 to 15 seconds or so that it was experienced.

The decompression incident on Kittinger’s balloon jump is discussed further in Shayler’s Disasters and Accidents in Manned Spaceflight: [When Kittinger reached his peak altitude] “his right hand was twice the normal size… He tried to release some of his equipment prior to landing, but was not able to as his right hand was still in great pain. He hit the ground 13 min. 45 sec. after leaving Excelsior. Three hours after landing his swollen hand and his circulation were back to normal.”

How long would a trip to Mars take?


Contrary to the ‘point and shoot’ idea, an actual trip to Mars looks very round-a-bout as the figure above shows for a typical ‘minimum cost’ trajectory. This, by the way, is called a Hohman Transfer Orbit, and is the mainstay of interplanetary space travel. All you need to do is give your payload a few km/sec of added speed at Earth to place you into the right elliptical orbit whose aphelion is at the location of mars, and then when you get there you fire your rockets in the opposite direction a second time to reduce your speed by a few km/sec to put you into a mars-capture orbit. You spend your entire flight coasting between the planets with no rockets firing. That’s what makes it a cheap flight in terms of fuel, but an expensive one in terms of flight time. In the end, it is always fuel cost that wins.

The travel time depends on the exact details of the orbit you take between the Earth and Mars. The typical time during Mars’s closest approach to the Earth every 1.6 years is about 260 days. Again, the details depend on the rocket velocity and the closeness of the planets, but 260 days is the number most often estimated, give or take 10 days. Some high-speed transfer orbits could make the trip in as little as 130 days.

That said, chemical rockets are very inefficient for interplanetary travel with specific impulses of about 250 seconds and maximum speeds of 10 km/sec. For some really quick trips ,engineers consider advanced ion propulsion systems with specific impulses of over 5000 seconds and maximum speeds of 100 km/sec and travel times of a month. Nuclear-thermal rockets can do even better with speeds up to 10,000 km/sec. At these speeds, a trip to Mars becomes less than a week!

An Old Era Ends-A New One is Born-Updated

As the international rush to get to the moon ramps up in the next few years, it is worth noting that, just as we are losing the World War II generation, we are also losing NASA’s early astronaut corps who made the 1960s and 1970’s space exploration possible.

Often called the most significant photo from space in human history, the famous “Earthrise” photo taken by Apollo 8 astronauts on Dec. 24, 1968 never fails to cause an emotional response. 

The Mercury, Gemini and Apollo astronauts are legends who made our current travel to the moon far less of a challenge 50 years later than it would otherwise have been. Since these missions completed their historic work, we have been able to mull over many scenarios for how to do it ‘right’ the next time, and so here we are. We have learned from our successes in science and engineering, but we have also learned from our failure of political nerve to go beyond the gauntlet thrown down by Apollo 17. Now we are in the midst of what appears to be a new Space Race, this time between the open societies of the ‘west’ and the closed and secretive society of China. Meanwhile, amidst this political hubris, the ranks of the Old Guard astronauts continue to thin out each year.

Project Mercury

The first group of astronauts to pass, were the original Project Mercury astronauts at the pionering, and very risky, dawn of NASA (1958-1963): Scott Carpenter, Gordon Cooper, John Glenn, Virgil Grisson, Walter Schirra, Alan Shepard and Donald Slayton. With the passing of John Glen in 2016 at the age of 95, we lost irretrivably our connection to the trials and tribulations of sitting in a ‘tin can’ as big as a telephone booth and eating food out of toothpaste tubes. These were the incredably brave men who sat on top of rockets that had only been tested a handful of times without blowing up!

John Glenn entering the Friendship 7 Mercury capsule on top of the Redstone rocket,

But more than that, these were the faces of NASA that we saw in the news media who made space travel a household word in the early-1960s. This was a HUGE transition in social consciousness because prior to Project Mercury, space travel was pure science fiction. We were a Nation obsessed by the prospects of nuclear war and Soviet spies lurking around every street corner. The adventures of the Mercury astronauts let hundreds of millions of people take a mental vacation and think about more hopeful ties to come. That plus the advent of the Jetsons TV series!

The 14 ‘Group 3’ astronauts selected in 1963 for the Gemini and Apollo manned programs

The second cohort of astronauts were those that flew with Project Gemini between 1963 and 1966. There were ten crewed missions and 16 astronauts, who conducted space walks, dockings and tested out technology and protocols for the Apollo program. Many of them went on to fly in Project Apollo having earned their ‘creds’ with Gemini.

The photo above shows, seated left to right, Edwin Aldrin (33), William Anders (30), Charles Bassett (32), Alan Bean (31), Eugene Cernan (29), and Roger Chaffee (28). Standing left to right are Michael Collins (33), Walter Cunningham (31), Donn Eisele (33), Theodore Freeman (33), Richard Gordon (34), Russell Schweickart (28), David Scott (31) and Clifton Williams (31). Additional astronauts were selected for Gemini: Frank Borman (35), Jim Lovell (35), Thomas Stafford (33), John Young (34), Neil Armstrong (33), and Pete Conrad (33). The ages of this group in 1963 spanned 29 to 35.

Whenever I look at this photo, I see these astronauts as being 10 years older than their actual age. I was a teenager during this time and anyone older than 25 or 30 looked pretty old to me. I guess for these astronauts, a military life, and the dress styles of the narrow-tie, conservative, early-60s does that to you.

NASA Astronaut Edward White floats in zero gravity of space northeast of Hawaii, on June 3, 1965, during the flight of Gemini IV.

At the present time, December 2024, the only survivors of the Mercury and Gemini groups are Edwin Aldrin (94), Russell Schweickart (89) and David Scott (92).

Finally, we have the Program Apollo astronauts. They were actually drawn from the Project Gemini group, but because of the premature deaths of Roger Chaffee, Ed White, Charles Bassett, and Theodore Freeman, additional astronauts were added to this project: Charles Duke, Harrison Schmitt, Ken Mattingly, Fred Haise, Wally Schirra, Edgar Mitchell, Jack Swigert, James Irwin, Alfred Wordon, James McDivitt, Ronald Evans, and Stuart Roosa.

50th Anniversary, 2019: From left to right: Charlie Duke (Apollo 16), Buzz Aldrin (Apollo 11), Walter Cunningham (Apollo 7), Al Worden (Apollo 15), Rusty Schweickart (Apollo 9), Harrison Schmitt (Apollo 17), Michael Collins (Apollo 11) and Fred Haise (Apollo 13). 
Felix Kunze/The Explorers Club

Each Apollo mission had three astronauts. Two would take the LEM to the surface for a walk-about, while the third astronaut remained behind in the Command Module. A total of 12 Apollo astronauts actually walked on the moon between Apollo 11 and 17: Neil Armstrong, Buzz Aldrin, Pete Conrad, Alan Bean, Alan Shepard, Edgar Mitchell, David Scott, James Irwin, John Young, Charles Duke, Eugene Cernan and Harrison Schmitt. Of these, the survivors by January, 2023 are Buzz Aldrin (92), David Scott (90), Charles Duke (87) and Harrison Schmitt (87).

An excellent view of the Lunar Excursion Module (LEM) “Orion” and Lunar Roving Vehicle (LRV), as photographed by astronaut Charles M. Duke Jr., lunar module pilot, during the first Apollo 16 extravehicular activity (EVA) at the Descartes landing site.

So, the surveying astronauts in December 2024 from the Mercury, Gemini and Apollo programs are, in order of age:

Buzz Aldrin (94: Gemini 12, Apollo 11),

David Scott (92: Gemini 8, Apollo 9, Apollo 15),

Fred Haise (91: Apollo 13),

Russell Schweickart (89: Apollo 9),

Charles Duke (89: Apollo 16)

Harrison Schmitt (89: Apollo 17).

Apollo 17 astronaut Harrison Schmitt on the moon.

We are entering something of a race against time for these survivors to be present for the launch of Artemus III. Artemis III is planned as the first crewed Moon landing mission of the Artemis program. Scheduled for launch in 2026, Artemis III is planned to be the second crewed Artemis mission and the first crewed lunar landing since Apollo 17 in 1972. Buzz Aldrin (92: Gemini 12, Apollo 11) was one of the first astronauts to set foot on the lunar surface, while Harrison Schmitt of Apollo 17 was one of the last. With Buzz Aldrin and David Scott, we even have survivors from the Gemini Program who laid the groundwork for EVAs (Gemini 12) and docking maneuvers (Gemini 8).

The odds are pretty good that many of these six Old Guard astronauts will still be with us to see the Artimus III lunar lander called Starship HLS reach the lunar surface, and oh what a celebration it will be at NASA!