# Artemis: A Technical Primer on the Return to the Moon > "We go to the Moon not because it is easy, but to learn how to stay." > — the operating premise of NASA's Artemis program, and the line that separates it > from Apollo. Apollo proved humans could reach the Moon and return. **Artemis** is built around a harder question: can we establish a *sustained* human presence there, and use it as a proving ground for Mars? This primer walks the architecture end to end — the launch stack, the trajectory, the orbital mechanics, and the surface objectives. --- ## 1. The program at a glance Artemis is sequenced as a series of increasingly ambitious missions: 1. **Artemis I** — an uncrewed shakedown. An SLS rocket sent an uncrewed Orion capsule on a 25.5-day flight around the Moon and back, splashing down in December 2022.[^a1] 2. **Artemis II** — the first crewed flight: a four-person lunar flyby on a free-return trajectory. Targeted for ~~September 2025~~ 2026 after schedule adjustments. 3. **Artemis III** — the first crewed landing since Apollo 17, targeting the lunar **south pole** using a commercial Human Landing System (HLS). The Artemis II crew has been assigned since 2023: Reid Wiseman (commander), Victor Glover (pilot), Christina Koch (mission specialist), and Jeremy Hansen (mission specialist, representing the Canadian Space Agency).[^crew] --- ## 2. Why the south pole? Apollo landed near the equator, in daylight, for operational simplicity. Artemis is going somewhere far less forgiving — and far more valuable. - **Water ice.** Permanently shadowed regions (PSRs) inside polar craters have not seen sunlight for billions of years. They are cold traps, and they hold water ice. - **Ice is infrastructure.** Split into hydrogen and oxygen, water becomes breathable air, drinking water, and rocket propellant — the difference between visiting and *staying*. - **Near-continuous power.** Some polar ridges sit in near-permanent sunlight, giving solar arrays a duty cycle the equator cannot match. The trade is brutal terrain, extreme thermal gradients, and long-shadow lighting that makes landing genuinely hard. --- ## 3. The launch stack: SLS and Orion The Space Launch System (SLS) Block 1 is the most powerful rocket NASA has flown since the Saturn V — but the two are not the same machine, and the differences are instructive. | Parameter | SLS Block 1 | Saturn V | | -------------------- | ------------------ | ------------------ | | Height | ~98 m (322 ft) | ~111 m (363 ft) | | Liftoff thrust | ~39.1 MN | ~35.1 MN | | Payload to TLI[^tli] | ~27 t | ~48 t | | Core stage engines | 4 × RS-25 | 5 × F-1 | | Boosters | 2 × 5-segment solid| none | | First flew | 2022 | 1967 | SLS actually *out-thrusts* Saturn V at liftoff, yet delivers barely half the payload toward the Moon. The reason is upper-stage energy: Saturn V's S-IVB was a heavyweight trans-lunar stage, while Block 1's interim upper stage is comparatively modest. Later SLS variants (Block 1B, Block 2) close that gap. The crew rides in **Orion**, a capsule for four, mated to a European Service Module built by Airbus that provides propulsion, power, and life-support consumables. --- ## 4. Mission architecture Unlike Apollo's direct lunar-orbit rendezvous, Artemis stages through a **Near-Rectilinear Halo Orbit (NRHO)** — a highly elliptical, energy-efficient orbit around the Moon that will eventually host the *Gateway* station. ```mermaid graph LR KSC[Earth · Kennedy] -->|SLS launch| LEO[Low Earth Orbit] LEO -->|TLI burn| COAST[Trans-Lunar Coast] COAST -->|insertion| NRHO[Near-Rectilinear Halo Orbit] NRHO -->|dock| GW[Gateway] NRHO -->|HLS descent| POLE[Lunar South Pole] POLE -->|ascent| NRHO NRHO -->|return burn| REENTRY[Earth Re-entry] ``` For Artemis III the crew launches on SLS, transfers to NRHO in Orion, docks with a pre-positioned HLS, descends to the surface, and later ascends to rejoin Orion for the ride home. The HLS and its propellant are delivered separately — decoupling the lander from the crew launch is what makes the architecture scalable. --- ## 5. The mathematics of getting there Every maneuver above is a change in velocity — a **delta-v** ($\Delta v$) — and each one is governed by the Tsiolkovsky rocket equation: $$\Delta v = I_{sp}\, g_0 \ln\!\left(\frac{m_0}{m_f}\right)$$ where $I_{sp}$ is specific impulse (s), $g_0 = 9.807\ \text{m/s}^2$, $m_0$ is the wet mass, and $m_f$ is the dry mass. The logarithm is the tyranny of the equation: because $\Delta v$ scales with $\ln(m_0/m_f)$, every additional increment of velocity costs *exponentially* more propellant. A rough delta-v budget for the outbound journey: | Maneuver | Approx. Δv | | -------------------------------- | ---------- | | Surface → Low Earth Orbit | ~9.4 km/s | | LEO → Trans-Lunar Injection | ~3.1 km/s | | Insertion into lunar NRHO | ~0.4 km/s | | NRHO → low lunar orbit → surface | ~2.5 km/s | Computing an ideal delta-v is a few lines: ```python from math import log def delta_v(isp_seconds: float, wet_mass: float, dry_mass: float, g0: float = 9.80665) -> float: """Ideal delta-v (m/s) from the Tsiolkovsky rocket equation.""" return isp_seconds * g0 * log(wet_mass / dry_mass) # A cryogenic upper stage (Isp ~ 465 s) burning off 80% of its mass: print(f"{delta_v(465, m0 := 100, mf := 20):.0f} m/s") # ≈ 7340 m/s ``` The 20% dry-mass fraction above yields roughly 7.3 km/s from a single stage — which is why lunar missions *stage*: you throw away empty tankage to keep the mass ratio favorable. --- ## 6. Surface objectives (Artemis III) The first crewed landing is a demonstration mission, not a full expedition — but its objectives set the template for everything that follows: - [x] Land two astronauts safely at the lunar south pole - [x] Demonstrate the Axiom AxEMU surface suit in a real EVA - [ ] Collect and characterize samples from a polar region, including possible ice - [ ] Deploy autonomous science instruments that outlive the crew's stay - [ ] Validate the NRHO-staged architecture for reuse on Artemis IV+ *(Checked items reflect capabilities already demonstrated on the ground or in prior missions; unchecked items are first-time surface objectives.)* --- ## 7. Open risks No honest program overview omits where it might slip: - **HLS readiness.** The lander is the long pole. Its development pace, not the rocket's, is the most likely driver of the landing date. - **Cryogenic propellant management.** Some architectures require storing and transferring cryogenic propellant in space for extended periods — a capability not yet demonstrated at operational scale. - **Suit delivery.** A new surface suit is on the critical path for the first EVA. - **Cadence.** "Sustained presence" demands roughly annual missions. Apollo proved a sprint; Artemis has to prove a rhythm. --- *Compiled as a PageVault example document.* 🌒 It exercises headings, tables, task lists, footnotes, math, a mermaid diagram, and a code block — the full markdown feature set — in a single self-contained file. [^a1]: Artemis I launched 16 November 2022 and splashed down 11 December 2022 after a flight of just over 25 days, validating the SLS/Orion stack and Orion's heat shield at lunar-return velocity (~11 km/s). [^tli]: **TLI** — Trans-Lunar Injection, the burn that raises an orbit from around Earth onto a trajectory toward the Moon. "Payload to TLI" is the standard yardstick for lunar-class launch capability. [^crew]: Crew assignment announced April 2023. Jeremy Hansen is the first non-American assigned to a lunar mission, flying under the NASA–CSA partnership.