How Space Exploration Works — and What's Next

On July 20, 1969, Neil Armstrong stepped onto the Moon. Twelve people walked on its surface between 1969 and 1972, and then nobody did for more than half a century. In April 2026, four astronauts flew around the Moon on Artemis II, the first crewed lunar flight of the new program. This article explains the physics that makes spaceflight so hard, how rocket economics changed in the past decade, what is in orbit now, and where the Moon, Mars, and the space station stand as of October 2026.

Key takeaways

• Reaching orbit is mostly about speed, not height. A spacecraft in low Earth orbit travels at roughly 7.8 kilometers per second (28,000 km/h), fast enough that it keeps falling around the planet instead of into it.
• The rocket equation punishes weight. Most of a rocket at liftoff is propellant, which is why rockets are built in stages and why payloads are a few percent of launch mass.
• Launch prices fell sharply. A NASA analysis put the Space Shuttle at about $54,500 per kilogram to orbit and Falcon 9's list price at about $2,720 per kilogram, a ratio of roughly 20 to 1.
• The Moon is back on the calendar. Artemis II flew in April 2026. Artemis III is now planned as a low Earth orbit docking test in 2027, and the first landing is planned for Artemis IV by 2028.
• Mars is a later chapter. Radiation, life support, and the cost of a round trip are unsolved, and the sample-return mission that would bring Martian rock to Earth was reported to have been effectively cancelled by Congress's January 2026 spending package.

Why getting to orbit is about speed, not height

The most common misunderstanding about spaceflight is that rockets go "up." Altitude is the easy part. The Kármán line, the conventional edge of space, sits at 100 kilometers, and a rocket can reach it and fall straight back down. Staying in space requires moving sideways, fast.

Newton's cannonball

Picture a cannon on a very tall mountain. Fire a ball gently and it lands nearby. Fire it harder and it lands farther away. Fire it hard enough and the ground curves away beneath it as fast as it falls, so it never lands. That is an orbit: continuous falling with a horizon that keeps retreating.

For low Earth orbit, "hard enough" means about 7.8 kilometers per second. NASA says the International Space Station travels at roughly five miles per second, completing an orbit in about 90 minutes, or 16 times a day. This is also why astronauts float. They are not beyond gravity. Gravity at the station's altitude is still strong, and the crew and the station are falling together.

The tyranny of the rocket equation

Getting a payload to that speed is expensive in a way that surprises people. In 1903, Konstantin Tsiolkovsky wrote down the relationship that governs every rocket: the change in speed equals the exhaust velocity times the natural logarithm of the ratio of starting mass to final mass. In symbols, Δv = ve × ln(m₀/mf).

The logarithm is the problem. Doubling your speed change at the same exhaust velocity does not double the required propellant. It squares the mass ratio. Here is a worked example, using round numbers. Reaching orbit takes roughly 9 to 10 km/s once you add the cost of fighting gravity and air drag to the 7.8 km/s orbital speed. A good kerosene-and-oxygen engine has an effective exhaust velocity of about 3 km/s. A single stage would then need a mass ratio of about e^(9.5/3), or around 24 to 1. That means about 96% of the vehicle at liftoff would be propellant, leaving 4% for the tanks, engines, and payload combined. The arithmetic here is ours, but it matches how real rockets turn out: the payload is a few percent of the launch mass.

Hiking offers a useful comparison. If you carry your own food for a week-long trek, a heavier pack makes you eat more, which makes you carry more food, and the loop compounds. A rocket carries fuel to lift the fuel that lifts the fuel.

Staging, and why rockets drop pieces

The practical fix is staging: drop the empty tanks and engines once they are used up so that the rest of the vehicle does not have to carry them. The Saturn V that sent Apollo to the Moon had three stages. Each one pushed the remaining stack to a higher speed before being discarded.

For more on the engines that make this possible, see our explainer on how rocket engines actually work, and our history of the rocket as an invention for how the technology got here.

Propellants compared

Different fuels trade performance against practicality.

Propellant pair	Used by	Strength	Weakness
Liquid hydrogen and liquid oxygen	Space Shuttle main engines, SLS core stage	Highest exhaust speed among common chemical propellants	Very low density, so tanks are huge; hard to store
Kerosene and liquid oxygen	Falcon 9	Dense, easy to handle, well understood	Lower exhaust speed than hydrogen; leaves soot that complicates reuse
Methane and liquid oxygen	Starship	Middle ground; cleaner burning; can in principle be made on Mars	Newer technology with less flight history

The methane choice for Starship is tied to a long-term idea: Mars has carbon dioxide in its atmosphere and water ice below the surface, which are the raw ingredients for methane and oxygen.

Where spacecraft go: the orbits that matter

Not all orbits are equal, and the altitude determines what a satellite can do.

Orbit	Altitude	Orbital period	Typical use
Low Earth orbit (LEO)	About 200 to 2,000 km	About 90 minutes at the station's altitude	Space station, Earth observation, Starlink
Medium Earth orbit (MEO)	About 2,000 to 35,000 km	Hours	GPS (about 20,200 km), Galileo, GLONASS, BeiDou
Geostationary orbit (GEO)	35,786 km	24 hours	Broadcast and weather satellites that appear fixed in the sky
Sun-Earth L2	About 1.5 million km	Moves with Earth around the Sun	James Webb Space Telescope

A geostationary satellite orbits once per day, so it stays over one spot on the equator. From that height, one satellite sees roughly 40% of the planet's surface. Our article on how satellites orbit Earth explains the physics, and the one on Lagrange points explains why a telescope can sit 1.5 million kilometers away without drifting off.

From Sputnik to Starship: a short history

The history of spaceflight divides into three eras: a Cold War race, a government-dominated middle period, and a commercial phase that is still taking shape.

Year	Milestone
1957	The Soviet Union launches Sputnik 1, the first artificial satellite
1961	Yuri Gagarin becomes the first person in space on April 12; Alan Shepard becomes the first American on May 5
1969	Apollo 11 lands on the Moon on July 20
1972	Apollo 17, the last crewed lunar landing
1981	First Space Shuttle flight; the program ran until 2011 and lost two orbiters, Challenger in 1986 and Columbia in 2003
1998	Construction of the International Space Station begins
November 2000	Continuous human presence on the station begins
2004	SpaceShipOne wins the $10 million Ansari X Prize for private suborbital flight
2008	SpaceX's Falcon 1 becomes the first privately developed liquid-fuel rocket to reach orbit
2015	A Falcon 9 first stage lands upright after launch, the first orbital-class booster to do so
2020	Crew Dragon carries NASA astronauts to the station, the first crewed U.S. launch since the Shuttle
April 20, 2023	First flight of Starship, which ended in failure
October 13, 2024	The Starship booster is caught by the launch tower on Flight 5
April 2026	Artemis II flies a crew around the Moon

Space historians sometimes point out that the most striking feature of this table is the gap. No one traveled beyond low Earth orbit between December 1972 and April 2026. The reasons were political and budgetary far more than technical, a point we return to below. For the scientific payoff of the first era, see our piece on the Apollo program's science legacy.

Why launching got cheaper

The most important change in the past decade is economic. A rocket's first stage holds most of its engines and most of its cost, so throwing it away after one use is like scrapping a jetliner after every flight. SpaceX began landing and reflying first stages in 2015, and the effect on prices has been large.

The numbers

A NASA analysis by Harry Jones estimated the Space Shuttle at about $1.5 billion per flight for 27,500 kg to orbit, or $54,500 per kilogram. It computed Falcon 9 at SpaceX's advertised $62 million for 22,800 kg, or about $2,720 per kilogram. That puts the Shuttle at roughly 20 times the cost per kilogram.

Some caution is needed. The Falcon 9 figure uses a list price and maximum payload, not actual cost, and a 2026 analysis noted that the list price has since risen to about $74 million. At that price, our arithmetic gives roughly $3,250 per kilogram. The Shuttle could also carry crew and cargo together, while Falcon 9 needs a separate capsule, which reduces payload. And a list price is what customers pay, not what it costs the company to fly.

What cheap launch changes

Lower prices make a new set of business models possible. Satellite constellations of thousands of spacecraft, which would have been uneconomical on expendable rockets, are now routine. The Space Foundation estimated the 2024 global space economy at $613 billion, up 7.8% from the year before, with the commercial sector responsible for about 78% of that growth. It also reported an orbital launch roughly every 28 hours in the first half of 2025.

Starship is designed to push this further. Full reusability, if achieved, could lower the cost again, though published targets for Starship's eventual price per kilogram are aspirations rather than results. As of October 2026, no Starship has been reused in the way a Falcon 9 booster is, and the vehicle has not yet demonstrated the key technique that its lunar and Mars plans depend on.

What is in orbit now

Orbit is getting crowded. The European Space Agency's 2025 Space Environment Report said about 40,000 objects are tracked by space surveillance networks, of which about 11,000 are active payloads, and estimated more than 1.2 million pieces of debris larger than 1 centimeter. ESA's 2026 report, which covers data through the end of 2025, said more than 300 launches put over 4,000 new payloads into orbit that year, and that on average more than three intact satellites or rocket stages re-enter the atmosphere every day while ten new payloads are launched.

Two practical points follow. First, a satellite count older than a year or two is probably out of date, because the active fleet has grown by thousands within a few years. Second, crowding is no longer an abstract risk. Our article on AI and space debris tracking covers how operators avoid collisions.

The station and its replacement

The International Space Station has been continuously occupied since November 2000. NASA describes a station with a mass of 419,725 kg, operated by five space agencies from 15 countries, with a crew of seven typically aboard. NASA's plan is to retire it around 2030. In June 2024, NASA awarded SpaceX a contract worth up to $843 million to build a U.S. Deorbit Vehicle, based on Dragon, to bring the station down in a controlled way over a remote ocean area. NASA plans to be a customer of commercial stations rather than an owner of its own.

For the station's science and daily life, see our explainer on the ISS, and for the systems that keep a crew alive, how astronauts survive in space.

The Moon: where Artemis stands in October 2026

NASA's Artemis program is the first serious attempt to return people to the Moon since Apollo. Its status changed considerably in 2026, so summaries written before that year are out of date.

What has flown

Artemis I, in November 2022, was an uncrewed test of the Orion capsule and the Space Launch System (SLS) rocket. Artemis II launched on April 1, 2026, and splashed down on April 10, a mission of 9 days, 1 hour, and 32 minutes, according to NASA. The crew were commander Reid Wiseman, pilot Victor Glover, mission specialist Christina Koch, and Jeremy Hansen of the Canadian Space Agency. It was the first crewed test of Orion and SLS.

What comes next

The plan has been reshuffled. According to a Congressional Research Service summary updated in June 2026, NASA now plans Artemis III for 2027 as a demonstration in low Earth orbit of one or both commercial Human Landing Systems, and Artemis IV, planned by 2028, as the first human landing since 1972. The original plan had Artemis III as the landing mission.

The reason is lander readiness. The two providers are SpaceX, with a version of Starship, and Blue Origin, with its Blue Moon lander. NASA's Office of Inspector General reported in March 2026 that both had faced delays and technical challenges. A Blue Origin rocket also exploded in May 2026, which raised concerns about the Artemis III and fall 2026 commercial-lander schedules.

The Gateway question

Gateway, a planned small station in lunar orbit, was to be a staging point with contributions from Canada and Japan. In 2026, NASA said it intends to pause Gateway in its current form and shift resources toward a lunar base, reusing equipment and partner commitments where possible. Congress has kept money flowing: the 2025 reconciliation law provided $6.7 billion for Orion, Gateway, and SLS through fiscal year 2032. The Government Accountability Office estimated cost overruns for three major Artemis projects at $6.8 billion in a 2025 report, and NASA requested $8.5 billion for Artemis systems in fiscal year 2027.

That budget background helps explain why Artemis is such an argument. SLS is expensive and flies rarely, while commercial vehicles promise a lower cost but have not yet flown a lunar mission. Our overview of the Artemis program goes deeper on the hardware.

Why the south pole

NASA's landing targets near the lunar south pole because permanently shadowed craters there hold water ice. Ice matters for the same reason water matters in the desert: it can be drunk, split into oxygen and hydrogen, or used as rocket propellant. Our article on why the Moon is more valuable than you think covers the resource case, and the one on lunar dust hazards covers a less-discussed engineering problem.

The rules and the rivals

The Artemis Accords are a set of non-binding principles for civil space exploration, launched in 2020 by the United States with seven other nations. They cover peaceful and transparent exploration, aid to people in distress, sharing scientific data, avoiding harmful interference, and protecting historic sites. NASA announced on September 28, 2026 that the total had reached 76 signatories.

China is pursuing its own program. Its Chang'e-6 mission collected 1,935.3 grams of samples from the far side of the Moon and returned them on June 25, 2024, a first for any country. China has also said it aims to put astronauts on the Moon before 2030, and it works on an International Lunar Research Station with partners outside the Accords.

Starship: the vehicle everyone is watching

Starship is a two-stage, fully reusable launch system, and the version flying in 2026, called Block 3, stands about 124 meters tall (408 feet), with 33 Raptor 3 engines on the booster. SpaceX quotes roughly 18 million pounds of thrust at liftoff, which is about 80 meganewtons, a figure we converted ourselves. By comparison, the Saturn V produced about 34 million newtons, so Starship is more than twice as powerful at liftoff.

The flight record shows a program making real progress with real problems.

Flight	Date	Outcome
1	April 20, 2023	Classed as a failure
5	October 13, 2024	First booster catch by the launch tower
12	May 22, 2026	First Block 3 flight; suborbital; booster lost in the Gulf, ship splashed down under control
13	July 24, 2026	Suborbital; same pattern of outcomes
14	September 28, 2026	First orbital flight; 26 Starlink V3 satellites deployed; one engine shut down early and the mission was cut short

Flight 15 was provisionally targeted for no earlier than November 8, 2026. Neither propellant transfer between two ships in orbit nor a ship catch had been demonstrated as of the latest reports. That matters because the lunar version of Starship needs to be refueled in orbit before it can go to the Moon. In plain terms, the plan requires launching several tanker flights to fill one lander, and the feasibility of that approach is the main technical question.

Our article on SpaceX Starship covers the design history in more detail.

Mars: the long-term goal

Mars attracts attention for several reasons. It has a day of 24.6 hours, a year of 687 Earth days, and a geology that shows signs of ancient water. Venus is closer to Earth at its nearest, but Mars has a surface a human could in principle land on and a plausible source of water and carbon dioxide.

The distance problem

Earth and Mars are as close as roughly 55 million kilometers and as far apart as roughly 400 million kilometers, depending on where each planet is in its orbit. Radio signals take between about 3 and 22 minutes one way, so a conversation with Mission Control is impossible. NASA's rovers show what a transit takes today: Perseverance launched on July 30, 2020, and landed on February 18, 2021, about 203 days later. Curiosity took about 254 days. Those durations are derived from the launch and landing dates NASA lists. Launch windows open only about every 26 months, when the planets are suitably aligned.

Why a human mission is hard

Challenge	Why it matters
Transit time	Six to nine months each way with chemical rockets, so crews are away for years
Radiation	Beyond Earth's magnetic field, astronauts receive more exposure over the long trip
Life support	Water and air must be recycled almost perfectly, with no resupply
Isolation	A small crew, a delay of minutes to talk to Earth, and no rescue
Landing	The thin atmosphere gives drag but not enough to slow a heavy vehicle with parachutes alone

Our article on the real challenges of living on Mars covers each of these, and the piece on Mars rovers shows what robots have learned in the meantime.

What robots have shown

The MOXIE instrument on Perseverance demonstrated that oxygen can be made from the Martian atmosphere. Across 16 runs it produced 122 grams of oxygen in total, about what a small dog breathes in 10 hours, and at its best reached 12 grams per hour at 98% purity. That is a small number, and it is also a proof of principle.

Perseverance has also been collecting rock samples in Jezero Crater, an ancient river delta, intended for return to Earth. That plan has hit a wall. Reports from January 2026 said Congress's spending package effectively cancelled Mars Sample Return as then formulated, after cost estimates ran to many billions of dollars and a return date in the late 2030s or later. The spending package had passed both chambers by mid-January 2026. The same legislation directed NASA to fund a Mars Future Missions line for technology that could support later robotic and crewed flights. The samples remain on Mars for now.

A realistic timeline

SpaceX has talked about crewed Mars flights on timelines that have repeatedly slipped, and the company's own schedule has proven aspirational rather than predictive. A crewed Mars landing in the 2030s would be a major achievement, and most analysts treat the 2040s as more realistic for a first attempt. These are judgments, not forecasts. They depend on Starship working, on in-orbit refueling succeeding, on funding, and on solving the radiation and life-support problems.

What people get wrong about space exploration

"Rockets are going to space to escape gravity." They are not. Gravity at orbital altitude is almost as strong as on the ground. What makes a satellite weightless is free fall.

"We stopped going to the Moon because we couldn't." The Apollo hardware was discontinued, and the expertise dispersed, mostly for political and budget reasons. Rebuilding that capability took decades, which is a large part of why Artemis is expensive.

"Reusable rockets make space cheap." They make it cheaper. A launch still costs tens of millions of dollars, and prices depend on how often rockets fly and what they carry.

"Mars is the nearest planet." Venus comes closer to Earth than Mars does. Mars is the most practical target for a surface mission.

"The ISS will last forever." NASA plans to retire it around 2030 and has contracted a vehicle to bring it down.

Frequently Asked Questions

Q: How fast must a spacecraft go to orbit Earth? A: About 7.8 kilometers per second (28,000 km/h) for low Earth orbit. NASA lists the International Space Station's speed as roughly five miles per second. Rockets must also overcome gravity and air drag on the way up, so the total speed change is closer to 9 to 10 km/s.

Q: Why do rockets have stages? A: Because of the rocket equation. Dropping empty tanks and engines means the rest of the vehicle no longer has to carry that weight, so the remaining propellant adds more speed. Without staging, payloads would be a tiny fraction of liftoff mass.

Q: When will humans land on the Moon again? A: NASA's plan, as summarized by the Congressional Research Service in June 2026, is for Artemis IV to attempt a landing by 2028, after Artemis III tests commercial landers in Earth orbit in 2027. Both dates depend on the readiness of the SpaceX and Blue Origin landers and could slip.

Q: How long does it take to reach Mars? A: NASA's recent robotic missions have taken roughly 200 to 255 days, for example about 203 days for Perseverance and 254 for Curiosity. Crewed missions with chemical rockets are expected to take six to nine months each way, and launch windows open about every 26 months. Nuclear thermal propulsion could shorten the trip, but it has not flown.

Q: Is there life on Mars? A: No confirmed evidence exists. Mars once had liquid water on its surface, and Perseverance is collecting samples in an ancient river delta for biosignature analysis. Without Mars Sample Return, the best laboratory analysis of those samples cannot yet happen on Earth.

Q: What are the Artemis Accords? A: A set of non-binding principles for civil lunar and space exploration, launched in 2020. NASA announced on September 28, 2026 that 76 countries had signed. China and Russia are not among them, and they are pursuing a separate lunar research station project.

Q: What happens to the International Space Station? A: NASA plans to retire and deorbit it around 2030 using a vehicle SpaceX is building under a contract worth up to $843 million, and to buy services from commercial stations instead.

The takeaway

Spaceflight is hard for a reason that does not change: reaching orbit means giving something 7.8 kilometers per second, and the rocket equation makes each extra kilometer per second cost far more than the last. What has changed is the economics. Reusing the most expensive part of the rocket cut launch prices by roughly a factor of 20 between the Shuttle era and Falcon 9, and that opened the door to constellations, commercial stations, and credible plans for a lunar base.

The honest picture in October 2026 is mixed. Artemis II proved that people can fly around the Moon again, and the landing has moved to a later mission. Starship has reached orbit and has not yet refueled in space. Mars remains a goal for the following decade or later. The question to ask of any space headline is not whether it is exciting but which unsolved step it depends on.

Sources

• NASA. Artemis II mission page.
• Congressional Research Service. Artemis: NASA's Program to Return Humans to the Moon. IF11643, updated June 25, 2026.
• NASA. Artemis Accords surpasses 75 signatories. September 28, 2026.
• NASA. International Space Station facts and figures.
• NASA. Mars exploration overview and Mars facts.
• Jones HW. "The Recent Large Reduction in Space Launch Cost." NASA Technical Reports Server, ICES-2018-81.
• Space Foundation. The Space Report 2025 Q2 (July 22, 2025), global space economy of $613 billion in 2024.
• European Space Agency. Space Environment Report 2026 and Space Environment Report 2025.
• Wikipedia. List of Starship launches, consulted for flight dates and outcomes.
• NASA Jet Propulsion Laboratory and MIT. MOXIE results on Perseverance.
• China National Space Administration, via the Chinese Academy of Sciences. Chang'e-6 sample return, June 2024.

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