Interview guides · Scout Space

Scout Space Software Engineer Interview Guide

Scout Space Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

At Scout Space, a Software Engineer—whether specializing as a Senior Flight Software Engineer or a Senior Mission Systems Engineer—builds the critical intelligence that powers the next generation of space domain awareness (SDA) and in-space observation systems. The software you write does not just run in a sterile cloud environment; it operates on physical hardware orbiting the Earth, processing real-time optical data, navigating complex orbital dynamics, and ensuring spacecraft safety. Your work directly impacts the safety and sustainability of space flight by enabling satellites to autonomously detect, track, and characterize orbital objects. This role sits at the highly demanding intersection of embedded systems, computer vision, and aerospace engineering.

This guide is scoped to a Software Engineer candidate at Scout Space.

Focus areas

Software Engineering (General)
Senior-Level Engineering
Mission Systems Engineering

The Scout Space interview process

Scout Space candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Conversation

Begin with understanding your background and experience.

What to demonstrate

Begin with understanding your background and experience
Depth in Software Engineering (General)

How to prepare

Answer aloud and timed: Explain how you would implement a lock-free ring buffer for passing telemetry data between a high-priority sensor interrupt and a lower-priority storage task.
Answer aloud and timed: What is priority inversion, and how does your choice of RTOS mitigate this issue when multiple tasks share a single SPI bus?

Technical Evaluations

Engage in deep technical evaluations focusing on real-world engineering scenarios.

What to demonstrate

Engage in deep technical evaluations focusing on real-world engineering scenarios
Depth in Software Engineering (General)

How to prepare

Answer aloud and timed: How would you design a software-based watchdog timer system to recover a microcontroller that has hung due to a single-event upset (SEU) in a high-radiation environment?
Answer aloud and timed: Describe the difference between stack and heap memory allocation in safety-critical systems. Why is dynamic memory allocation often banned in flight software?

Onsite Panel Preparation

Prepare for deep-dive architecture and behavioral evaluations as you approach the onsite panel.

What to demonstrate

Prepare for deep-dive architecture and behavioral evaluations as you approach the onsite panel
Depth in Software Engineering (General)

How to prepare

Answer aloud and timed: How do you write code to ensure determinism? What constructs in C++ can introduce non-deterministic execution times?
Answer aloud and timed: Write a function in Python or C++ to propagate a satellite's state vector over a short time interval using basic Keplerian elements.

Final Decision

Receive a final decision typically within a few weeks.

What to demonstrate

Receive a final decision typically within a few weeks
Depth in Software Engineering (General)

How to prepare

Answer aloud and timed: How would you architect a data pipeline to ingest high-frequency image data from an optical payload, perform onboard object detection, and compress the output for downlink?
Answer aloud and timed: Describe how you would implement a Kalman filter to estimate the position and velocity of a target spacecraft using noisy range and bearing measurements.

Where candidates lose points

Think like a hardware engineer

When writing code or designing systems, always consider the physical hardware. Mention CPU cycles, memory footprints, power consumption, and thermal constraints.

Emphasize testing and validation

Space missions do not get a second chance. Always discuss how you would test your code, build simulation harnesses, and validate edge cases using HIL setups.

Communicate across disciplines

Show that you can speak the language of electrical and mechanical engineers. Use clear, unambiguous terminology when discussing interfaces and data structures.

Questions & practice

Explain how you would implement a lock-free ring buffer for passing telemetry data between a high-priority sen

Medium · Embedded Systems & Flight Software

Explain how you would implement a lock-free ring buffer for passing telemetry data between a high-priority sensor interrupt and a lower-priority storage task.

Approach

Say what the runtime actually does before reasoning about the code.
Name what is shared across threads and what owns each piece of state.
Identify the window where an invariant is briefly untrue.
Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

What happens if two callers reach this at the same time?
Where could this allocate more than you expect?

Describe the difference between stack and heap memory allocation in safety-critical systems. Why is dynamic me

Medium · Embedded Systems & Flight Software

Describe the difference between stack and heap memory allocation in safety-critical systems. Why is dynamic memory allocation often banned in flight software?

Approach

Say what the runtime actually does before reasoning about the code.
Name what is shared across threads and what owns each piece of state.
Identify the window where an invariant is briefly untrue.
Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

What happens if two callers reach this at the same time?
Where could this allocate more than you expect?

Collapse a redelivered event batch into per-aggregate high-water marks

Easy · hashing · at-least-once · aggregation

You drain a batch of up to 5,000,000 events, each (aggregate_id BIGINT, aggregate_version INT, event_type, payload). The log guarantees order within one aggregate only; the batch merges 64 partitions, and a relay failover has redelivered a range, so an older version for an aggregate can appear after a newer one. Given a map of last_applied_version per aggregate, produce the events worth applying, at most one per (aggregate_id, version), plus the count discarded. Target O(n) time. State the memory for 2,000,000 distinct aggregates and what you do when it does not fit.

Approach

One pass, one hash map from aggregate_id to the highest version kept, and a discard counter. An event whose version is at or below last_applied_version for its aggregate is dropped without further work, which is the whole reason the event carries its version rather than a delta. O(n) expected time, O(d) space in distinct aggregates.
Keep the maximum, never the last occurrence. The redelivered range means the final appearance of an aggregate in the batch can be an older version than one seen earlier in the same batch, so last-wins applies stale state over newer state and the projection regresses with no error anywhere.
Cost the memory instead of calling it large: an 8-byte key plus a 4-byte version is 12 bytes of payload, and an open-addressed table held at a 0.7 load factor costs roughly 17 bytes per entry before per-slot metadata, so 2,000,000 aggregates is tens of megabytes in a native layout and several times that in a runtime that boxes both key and value.
If the distinct set exceeds memory, partition on hash(aggregate_id) mod P and reduce each partition independently. Every event for one aggregate hashes to the same partition, so the per-partition result is exact and the merge is concatenation rather than a second reduction.

Follow-up

The payload is a patch rather than a snapshot, so applying only the highest version loses the intermediate changes. What changes in your reduction?
How do you detect that version 7 arrived while version 6 was never delivered, and what should the consumer do about the gap?

Write the update path that detects a concurrent edit

Medium · optimistic concurrency · transactional outbox · audit history

resource carries version INT NOT NULL DEFAULT 1. resource_revision holds revision_id, resource_id, version, actor_user_id, change_kind, patch JSONB, request_id, created_at with UNIQUE (resource_id, version). outbox_event holds aggregate_type, aggregate_id, aggregate_version, event_type, payload, status. A PUT carries the version the client read. Write the exact statements for the single transaction that applies the edit, records the revision and enqueues 'resource.updated', and give the handler's branch on zero affected rows. Then say what PostgreSQL 16 does under READ COMMITTED when two of these updates hit one row at once.

Approach

One transaction, three writes, no network call inside it: UPDATE resource SET title = $3, version = version + 1, updated_at = now() WHERE resource_id = $1 AND tenant_id = $4 AND version = $2; then INSERT the resource_revision row at version $2 + 1; then INSERT the outbox_event row at the same aggregate_version. The event goes to a table rather than a broker because no transaction spans both.
Branch on the affected-row count before doing anything else. Zero has three causes — stale version, wrong tenant, row gone — so re-read once and map to 409 carrying the current version, or 404 for an id outside the caller's tenant, which also stops the endpoint confirming that another tenant's id exists.
State the engine behaviour instead of assuming it. Under READ COMMITTED the second UPDATE blocks on the row lock, and when the first commits PostgreSQL re-evaluates the WHERE clause against the newly committed row, so the version predicate now fails and the statement reports zero rows. Under REPEATABLE READ the identical collision raises SQLSTATE 40001 instead, so the handler must fold both shapes into one conflict response.
Keep UNIQUE (resource_id, version) even though the predicate already serialises writers. It is what makes a lost update unwritable if any other path ever reaches the revision table, and it converts a logic bug into 23505 rather than into a silently missing history row.

Follow-up

A client sends the version it read ten minutes ago and the resource has moved three versions. What is in your 409 so it can resolve the conflict without a full re-fetch?
Two editors, two disjoint fields, no overlap. Does your answer still refuse the second write, and should it?

Find version gaps and relay lag with window functions

Medium · window functions · event tables · frame semantics

outbox_event holds event_id, aggregate_type, aggregate_id, aggregate_version, event_type, payload, status ('pending','published','dead'), attempts, created_at, published_at. A projection is missing rows and you must decide whether the relay skipped events or the consumer dropped them. Write three queries over the last seven days: one listing every aggregate_id whose published aggregate_version sequence has a hole, one giving per-day counts with a running total, and one returning the newest published event per aggregate. For each, say where the window function is evaluated relative to WHERE and LIMIT. PostgreSQL 16.

Approach

Gaps: compute lead(aggregate_version) OVER (PARTITION BY aggregate_id ORDER BY aggregate_version) in a subquery, then filter next_version <> aggregate_version + 1 in the outer query. Window functions are evaluated after WHERE, GROUP BY and HAVING and before the outer ORDER BY and LIMIT, so the predicate cannot sit in the same WHERE clause and PostgreSQL 16 has no QUALIFY.
Say what the seven-day filter does to the answer: it truncates every partition, so the first row per aggregate has no predecessor inside the window and a hole spanning the boundary is invisible. Widen the window, or join to resource.version as the authority for the true maximum.
Running total: SELECT date_trunc('day', created_at) AS d, count() AS n, sum(count()) OVER (ORDER BY date_trunc('day', created_at) ROWS UNBOUNDED PRECEDING). An aggregate inside a window call is legal because grouping runs before windowing. The grouping key is unique per row here so ROWS and RANGE agree, but write the frame anyway — over ungrouped rows with tied timestamps the default RANGE frame pulls in every peer row and the total jumps.
Newest per aggregate: DISTINCT ON (aggregate_id) ... ORDER BY aggregate_id, aggregate_version DESC is the cheap PostgreSQL-only form when an index matches that order; row_number() OVER (PARTITION BY aggregate_id ORDER BY aggregate_version DESC) = 1 is the portable form and needs a subquery for the same evaluation-order reason as the gap query.

Follow-up

Relay failover redelivers events. Does a duplicate break the gap query, and how would you detect one from this table alone?
Turn the gap check into a continuous monitor rather than a query someone runs after an incident. What does it watch?

What is priority inversion, and how does your choice of RTOS mitigate this issue when multiple tasks share a s

Medium · Embedded Systems & Flight Software

What is priority inversion, and how does your choice of RTOS mitigate this issue when multiple tasks share a single SPI bus?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

How would you design a software-based watchdog timer system to recover a microcontroller that has hung due to

Medium · Embedded Systems & Flight Software

How would you design a software-based watchdog timer system to recover a microcontroller that has hung due to a single-event upset (SEU) in a high-radiation environment?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

How do you write code to ensure determinism? What constructs in C++ can introduce non-deterministic execution

Medium · Embedded Systems & Flight Software

How do you write code to ensure determinism? What constructs in C++ can introduce non-deterministic execution times?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

Write a function in Python or C++ to propagate a satellite's state vector over a short time interval using bas

Medium · Mission Systems & Orbital Math

Write a function in Python or C++ to propagate a satellite's state vector over a short time interval using basic Keplerian elements.

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

How would you architect a data pipeline to ingest high-frequency image data from an optical payload, perform o

Medium · Mission Systems & Orbital Math

How would you architect a data pipeline to ingest high-frequency image data from an optical payload, perform onboard object detection, and compress the output for downlink?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

Describe how you would implement a Kalman filter to estimate the position and velocity of a target spacecraft

Medium · Mission Systems & Orbital Math

Describe how you would implement a Kalman filter to estimate the position and velocity of a target spacecraft using noisy range and bearing measurements.

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

Given a coordinate transformation from the camera's body frame to the spacecraft's inertial frame, how do you

Medium · Mission Systems & Orbital Math

Given a coordinate transformation from the camera's body frame to the spacecraft's inertial frame, how do you project a detected pixel coordinate into a 3D unit vector?

Approach

Clarify what is being asked and what a complete answer contains.
State your assumptions explicitly before working the problem.
Say what you would check first and why it is the highest-information step.
Work from the requirement backwards to the design.

Follow-up

What assumption would you test first?
How would you know your answer was wrong?

How would you structure a Hardware-in-the-Loop (HIL) testing framework to validate flight software against sim

Medium · System Design & Fault Tolerance

How would you structure a Hardware-in-the-Loop (HIL) testing framework to validate flight software against simulated sensor inputs?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

Describe your strategy for implementing a "Safe Mode" transition. What criteria should trigger this mode, and

Medium · System Design & Fault Tolerance

Describe your strategy for implementing a "Safe Mode" transition. What criteria should trigger this mode, and how do you ensure the software remains responsive?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

How do you design a distributed logging system across multiple onboard computers where storage space is highly

Medium · System Design & Fault Tolerance

How do you design a distributed logging system across multiple onboard computers where storage space is highly constrained?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

How would you handle a scenario where an optical sensor starts outputting corrupted data packets due to an ele

Medium · System Design & Fault Tolerance

How would you handle a scenario where an optical sensor starts outputting corrupted data packets due to an electrical fault?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

Give an example of a project where requirements changed late in the development cycle. How did you adapt your

Medium · Behavioral & Mission Alignment

Give an example of a project where requirements changed late in the development cycle. How did you adapt your architecture to accommodate the change?

Approach

Fix the scope first: who calls this, how often, and what they do when it fails.
Name the read and write paths separately; they rarely have the same bottleneck.
Choose a partition key and say what query it makes expensive.
State the consistency you need, and where you are willing to be stale.

Follow-up

What breaks first when traffic grows ten times?
How does this behave when that dependency is down for an hour?

Design the telemetry and command handling architecture for a satellite payload. How do you guarantee that crit

Medium · System Design & Fault Tolerance

Design the telemetry and command handling architecture for a satellite payload. How do you guarantee that critical commands are executed even during intermittent radio contact?

Approach

Establish what changed and when, before forming any theory.
Pick a bisection that eliminates candidates whichever way it turns out.
Check the instrumentation before believing the symptom.
Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

What would you look at first, and what would it rule out?
How would you tell a cause from a coincidence here?

Describe a situation where you had to debug a software issue that only occurred when integrated with physical

Medium · Behavioral & Mission Alignment

Describe a situation where you had to debug a software issue that only occurred when integrated with physical hardware. How did you isolate the problem?

Approach

Establish what changed and when, before forming any theory.
Pick a bisection that eliminates candidates whichever way it turns out.
Check the instrumentation before believing the symptom.
Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

What would you look at first, and what would it rule out?
How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics Scout Space candidates report.

Day 1 — Map the Scout Space loop

Write out the reported sequence: Initial Conversation, Technical Evaluations, Onsite Panel Preparation, Final Decision.
For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Software Engineering (General)

Spend the session on Software Engineering (General), which Scout Space candidates report being tested on.
Write one worked example in Software Engineering (General) and time yourself on it.

Deliverable: One timed worked example in Software Engineering (General).

Day 3 — Work Senior-Level Engineering

Spend the session on Senior-Level Engineering, which Scout Space candidates report being tested on.
Write one worked example in Senior-Level Engineering and time yourself on it.

Deliverable: One timed worked example in Senior-Level Engineering.

Day 4 — Work Mission Systems Engineering

Spend the session on Mission Systems Engineering, which Scout Space candidates report being tested on.
Write one worked example in Mission Systems Engineering and time yourself on it.

Deliverable: One timed worked example in Mission Systems Engineering.

Day 5 — Answer out loud: Embedded Systems & Flight Software

Answer aloud, timed: Explain how you would implement a lock-free ring buffer for passing telemetry data between a high-priority sensor interrupt and a lower-priority storage task.
Answer aloud, timed: What is priority inversion, and how does your choice of RTOS mitigate this issue when multiple tasks share a single SPI bus?

Deliverable: Spoken answers to 2 reported Embedded Systems & Flight Software question(s), under time.

Day 6 — Answer out loud: Mission Systems & Orbital Math

Answer aloud, timed: Write a function in Python or C++ to propagate a satellite's state vector over a short time interval using basic Keplerian elements.
Answer aloud, timed: How would you architect a data pipeline to ingest high-frequency image data from an optical payload, perform onboard object detection, and compress the output for downlink?

Deliverable: Spoken answers to 2 reported Mission Systems & Orbital Math question(s), under time.

Day 7 — Answer out loud: System Design & Fault Tolerance

Answer aloud, timed: Design the telemetry and command handling architecture for a satellite payload. How do you guarantee that critical commands are executed even during intermittent radio contact?
Answer aloud, timed: How would you structure a Hardware-in-the-Loop (HIL) testing framework to validate flight software against simulated sensor inputs?

Deliverable: Spoken answers to 2 reported System Design & Fault Tolerance question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

How do you handle coordinate system transitions (e.g., ECI to ECEF) in a high-performance simulation environme

Medium · Mission Systems & Orbital Math

How do you handle coordinate system transitions (e.g., ECI to ECEF) in a high-performance simulation environment?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

Tell me about a time you had to make a trade-off between software performance and code readability. What was t

Medium · Behavioral & Mission Alignment

Tell me about a time you had to make a trade-off between software performance and code readability. What was the outcome?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?

How do you approach working with non-software engineers, such as Satellite Electrical Engineers, to define har

Medium · Behavioral & Mission Alignment

How do you approach working with non-software engineers, such as Satellite Electrical Engineers, to define hardware-software interface specifications?

Approach

Pick a story where you made the decision, not one where you watched it.
State the situation in two sentences and spend the rest on the reasoning.
Give the blast radius: what could have broken, and what you measured.
Name the disagreement and how you resolved it with evidence.

Follow-up

What would you do differently if you ran that again?
How did you know your change caused the improvement?