Space Time · Guided activity · 5–10 min

Why does a reply from Voyager take so long?

Distinguish a calculated light-travel time from a reported radio contact.

Name: ____________________ Date: ____________________

In the spacecraft fleet, open Explore a question and Your Voyager response. Save your prediction, record the position and DSN report separately, then explain what they establish. Keep a copy in a collection to export, print or resume. No account is required.

  1. Before inspecting the fleet, predict what determines how long a reply from Voyager 2 takes. Open Your Voyager response to keep your reasoning in this browser.
  2. Find Voyager 2. Record its Earth distance, one-way light time and position sample date. If a value is unavailable, leave it unknown.
  3. Double the one-way time for a simplified signal round trip. This assumes an immediate reply and ignores motion during transit.
  4. Read the DSN report separately. Record its source time and whether it reports an uplink, downlink, no contact, or unavailable data.

Explain using evidence

Does a calculated travel time prove that Voyager is communicating right now?

Record unknown values as unknown. The app uses a nearby Horizons position sample. Twice its one-way time is an estimate, not a measured command-response delay or communication schedule.

Teacher notes & answer discussion

Have learners label each entry calculated, reported or unknown. Compare timestamps before comparing numbers. Accept unknown as a valid result when either service is unavailable; do not supply fictional replacement readings. Use Your Voyager response in the spacecraft fleet to save prediction, observation, explanation and separate position/contact records. Refreshing live data keeps saved evidence; recording again replaces it. Keep a copy in a collection to export, print or resume.

No. Distance divided by light speed estimates propagation time. A DSN snapshot reports ground-station signal activity at its own timestamp. Neither a missing entry nor an old report establishes that the spacecraft has failed.

Discussion checklist

  • A prediction is recorded before inspecting Voyager 2.
  • The position sample, calculated one-way time and simplified round trip are distinguished from reported DSN activity.
  • Both records retain their own timestamps and limitations, or explicitly say unknown.
  • The explanation revisits the prediction and avoids treating a missing or old contact report as evidence of spacecraft failure.

Twice the one-way estimate assumes an immediate reply and ignores spacecraft motion. Ask for timestamped evidence when the response claims current communication. This checklist supports discussion; it is not an automated grade.

Sources

Editorial activity reviewed September 21, 2026. Suggested duration is approximate. No curriculum certification is claimed.