雅思阅读 068 — Can NASA Launch a Nuclear Mission to Mars by 2028?

改编自 Scientific American（2026-03，David W. Brown）。

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When NASA announced a new Mars helicopter mission called Skyfall, the bigger, more shocking news was that it would fly to Mars on a first-of-its-kind nuclear-propelled spacecraft.

"After decades of study and billions spent on concepts that have never left Earth, America will finally get underway on nuclear power in space," said NASA administrator Jared Isaacman during the announcement.

The reveal stunned the U.S. planetary science community, whose official list of recommended future missions had not mentioned a nuclear-powered mission to Mars. In spaceflight terms, late 2028 is practically tomorrow, setting a tight deadline even without the added complexity of nuclear propulsion.

Skyfall is intended to reach Mars using a small, 20-kilowatt nuclear-powered spacecraft called Space Reactor-1 (SR-1) Freedom. NASA is taking the lead and acting as the spacecraft's "prime integrator" in partnership with the Department of Energy, which handles U.S. nuclear stockpiles. Many elements of the spacecraft and reactor are either deep into development or already built, Isaacman said.

Even so, the reactor itself has not been built. SR-1 Freedom will rely on nuclear electric propulsion: it will convert heat from its nuclear reactor into electricity to power xenon gas thrusters that produce no radioactive exhaust. Unlike nuclear thermal propulsion, which vent radioactive exhaust at temperatures above 4,400 degrees Fahrenheit, nuclear electric propulsion runs continuously but low and slow, building great speeds over years.

The reactor will be fuelled by high-assay, low-enriched uranium — borrowing an approach from an ill-fated earlier project called DRACO. Conceived in 2023, DRACO was a half-billion-dollar crash programme to launch a nuclear thermal propulsion rocket by 2027 at the earliest. Using a larger amount of low-enriched uranium rather than a smaller amount of highly enriched weapons-grade stuff was meant to sidestep regulatory red tape. But in 2024, the Department of Energy added a requirement for ground testing, which would take years and hundreds of millions of dollars. DARPA abandoned the project in 2025.

"In many ways, DRACO was a half-technical, half-regulatory pilot programme," says Scott Pace, director of the Space Policy Institute at George Washington University. "I regretted its cancellation, as we lost an opportunity to pilot the regulatory approval process for putting a nuclear reactor in space."

A history of setbacks

The legacy of nuclear propulsion is deep and star-crossed. In 1961, President John F. Kennedy committed funds to accelerate the development of a nuclear rocket, promising "some day providing a means for even more exciting and ambitious exploration of space, perhaps beyond the moon".

In 1965, the U.S. launched SNAP-10A, which, to date, remains the nation's only nuclear reactor to reach orbit. A predecessor, SNAP-9A, released about a kilogram of radioactive plutonium into the atmosphere after it failed to reach orbit in 1964. Several Soviet space reactors have also contaminated Earth with fissile material. Antinuclear public sentiment, budget cuts and regulatory challenges have scuttled subsequent U.S. space reactor programmes.

Doubts about the plan

Not everyone is sanguine about NASA's latest likelihood of success. Andrew Higgins, an aerospace engineer at McGill University, worries that the LEGO-like way SR-1 Freedom has been planned — with parts from different, unrelated projects bolted together — vastly understates the challenge.

"Mars is too nearby for SR-1 Freedom to flex its muscles and build up high speed," Higgins says. "If you're orbiting several moons of Jupiter or going to Neptune's moon Triton, then nuclear electric propulsion makes sense. But for Mars, solar power is far more efficient."

Why Skyfall, then? The helicopters are basically print-to-order, and the mission won't require a separate lander. SR-1 Freedom makes no sense for Skyfall, but Skyfall wouldn't exist without SR-1 Freedom. Each, by necessity, hoists the other out of abject improbability.

A December 2028 deadline also coincides with the last month of the Trump administration's term in office — timing that could help sustain White House support and defend against any congressional cancellation attempts.

"Suppose it all worked, but it launched two years behind schedule," a former NASA official says. "You think that would be a horrible failure? We would have nuclear electric propulsion! I would be cheering up and down."

Questions

Questions 1–5: TRUE / FALSE / NOT GIVEN

1. Skyfall is the first nuclear-propelled spacecraft NASA has announced.
2. SR-1 Freedom's reactor has already been built.
3. Nuclear electric propulsion produces no radioactive exhaust.
4. DRACO was successfully launched in 2027.
5. SNAP-10A was the only U.S. nuclear reactor to reach orbit.

Questions 6–10: Choose the correct letter, A, B, C or D.

6. Skyfall's mission is to send what to Mars?

   • A. Astronauts
   • B. Robotic helicopters
   • C. A rover
   • D. A space station

7. How powerful is the SR-1 Freedom reactor?

   • A. 200 kilowatts
   • B. 20 kilowatts
   • C. 2 kilowatts
   • D. 200 megawatts

8. Why was DRACO cancelled?

   • A. It was too expensive to build.
   • B. The DOE required ground testing, which would delay it for years.
   • C. Congress voted against it.
   • D. The rocket exploded on the launch pad.

9. Andrew Higgins argues that for Mars missions,

   • A. nuclear propulsion is essential
   • B. solar power is more efficient than nuclear electric propulsion
   • C. nuclear propulsion reduces launch costs
   • D. astronauts should be sent first

10. The December 2028 launch deadline was chosen partly because

    • A. it is the next Mars launch window
    • B. it coincides with the end of the Trump administration, helping sustain political support
    • C. the reactor will be ready by then
    • D. the helicopters require a specific season

Questions 11–13: Complete the sentences. Choose NO MORE THAN TWO WORDS.

11. Skyfall uses __________ propulsion, converting reactor heat into electricity to drive xenon thrusters.
12. DRACO was a joint programme between NASA and __________.
13. The former NASA official said even a two-year delay would be a success because it would demonstrate __________ propulsion.

Answers

1. TRUE
2. FALSE (尚未建造)
3. TRUE
4. FALSE (2025 年取消)
5. TRUE
6. B
7. B
8. B
9. B
10. B
11. nuclear electric
12. DARPA
13. nuclear electric

Glossary

• propulsion /prəˈpʌlʃn/ n. 推进
• reactor /riˈæktə/ n. 反应堆
• enriched uranium /ɪnˈrɪtʃt ˈjuːreɪniəm/ n. 浓缩铀
• xenon /ˈzenɒn/ n. 氙
• thruster /ˈθrʌstə/ n. 推进器
• fissile /ˈfɪsaɪl/ adj. 可裂变的
• regulatory /ˈreɡjələtri/ adj. 监管的
• abject /ˈæbdʒekt/ adj. 绝望的
• prime integrator /praɪm ˈɪntɪɡreɪtə/ n. 主集成商