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Orbex Group Software Engineer Interview Guide

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

The 60-second brief

At Orbex Group, a Software Engineer plays a pivotal role in pioneering the future of sustainable spaceflight. The software you write directly controls, monitors, and validates the orbital launch vehicles designed to deliver small satellites into low Earth orbit. From the low-level embedded systems controlling the Orbex Prime rocket's propulsion systems to the ground segment software managing telemetry and launchpad communications, your code is a critical element of launch success. This role demands an exceptional level of precision, as software failures in aerospace can have catastrophic consequences. You will work on highly complex, real-time distributed systems where low latency, safety-critical design, and deterministic behavior are standard requirements.

This guide is scoped to a Software Engineer candidate at Orbex Group.

Focus areas

  • Propulsion systems (software responsibility)
  • Technical interview discussion
  • Embedded systems architecture

The Orbex Group interview process

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

Initial Screening Call

A conversation with HR to align on background, career goals, salary expectations, and role duties.

What to demonstrate

  • A conversation with HR to align on background, career goals, salary expectations, and role duties
  • Depth in Propulsion systems (software responsibility)

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Evaluation

Conversational interviews focusing on past projects, architectural decisions, and technical expertise.

What to demonstrate

  • Conversational interviews focusing on past projects, architectural decisions, and technical expertise
  • Depth in Propulsion systems (software responsibility)

How to prepare

  • Answer aloud and timed: How would you debug a race condition or a deadlock in a multi-threaded embedded application?
  • Answer aloud and timed: Describe your experience with hardware communication protocols such as SPI, I2C, CAN bus, or Ethernet in an aerospace context.

Meeting with Software Lead

Discussion with the Software Department Lead to assess technical fit and expertise.

What to demonstrate

  • Discussion with the Software Department Lead to assess technical fit and expertise
  • Depth in Propulsion systems (software responsibility)

How to prepare

  • Answer aloud and timed: How do you optimize C/C++ code for execution speed and minimal memory footprint on resource-constrained microcontrollers?
  • Answer aloud and timed: How would you design a telemetry ingestion pipeline that must process high-frequency data streams from the rocket during launch?

Technical Panel Interview

In-depth discussions with a panel including embedded systems and engineering specialists.

What to demonstrate

  • In-depth discussions with a panel including embedded systems and engineering specialists
  • Depth in Propulsion systems (software responsibility)

How to prepare

  • Answer aloud and timed: Describe how you structure software to handle network latency and packet loss between the ground station and the vehicle.
  • Answer aloud and timed: What architectural patterns do you use to ensure loose coupling and high testability in a large-scale software system?

Where candidates lose points

Focus on the "Why" behind your decisions

When describing past projects, don't just explain what you built. Explain why you chose a specific language, architecture, or protocol, and what trade-offs you considered.

Emphasize safety and reliability

Whether you are writing flight software or ground tools, always highlight how you test your code, handle errors, and design for failure recovery.

Prepare to discuss hardware-software boundaries

Be ready to talk about how your software interacts with physical systems. If you have experience with oscilloscopes, logic analyzers, or HIL setups, make sure to mention it.

Questions & practice

How do you manage memory allocation in a safety-critical, real-time system where dynamic allocation is prohibi

Medium · Embedded & Real-Time Systems

How do you manage memory allocation in a safety-critical, real-time system where dynamic allocation is prohibited?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. 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?

How would you debug a race condition or a deadlock in a multi-threaded embedded application?

Medium · Embedded & Real-Time Systems

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. 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?

How do you optimize C/C++ code for execution speed and minimal memory footprint on resource-constrained microc

Medium · Embedded & Real-Time Systems

How do you optimize C/C++ code for execution speed and minimal memory footprint on resource-constrained microcontrollers?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. 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?

Hold a per-tenant active cap against concurrent creates

Hard · write skew · isolation levels · constraints

A tenant on the standard plan may hold at most 50 resources with status='active'. The create handler runs SELECT count(*) FROM resource WHERE tenant_id = $1 AND status = 'active', compares to 50, then inserts. Two creates arrive 3 ms apart on different instances and the tenant lands at 51. Name the anomaly, say whether PostgreSQL 16 READ COMMITTED or REPEATABLE READ prevents it and why, then give an implementation that holds the cap at READ COMMITTED with the exact statements. Finally, say what changes when the cap is 'at most one running export per tenant' on job_run.

Approach

  1. Name it: write skew. The two transactions read an overlapping set and write disjoint rows, so there is no row-level conflict for the engine to detect and each commit is individually legal.
  2. Rule out the levels precisely. READ COMMITTED takes a fresh snapshot per statement and takes no lock on the counted rows, so both see 49. PostgreSQL's REPEATABLE READ is snapshot isolation: it removes non-repeatable reads and phantoms within the snapshot but still admits write skew, because the anomaly is not a re-read of a changed row, it is a read of a set that a concurrent transaction invalidates. Only SERIALIZABLE closes it, by tracking the read dependency and aborting one transaction with SQLSTATE 40001 — a guarantee that exists only if the application re-runs the whole transaction from the read.
  3. Convert the set predicate into a single-row conflict: keep tenant.active_resource_count and run UPDATE tenant SET active_resource_count = active_resource_count + 1 WHERE tenant_id = $1 AND active_resource_count < 50 in the same transaction as the INSERT. Zero affected rows is the cap, returned as 409. The row lock serialises the decision at any isolation level, and contention is bounded to one tenant's row — which is also the fair-scheduling unit, unlike a global counter that would convoy every tenant behind one row.
  4. State the cost you just took on: a counter is a second source of truth that can drift, so every path that changes status must adjust it inside the same transaction, and a periodic reconciliation has to exist, with resource_revision as the authority for what the count should have been.

Follow-up

  • A resource moves from archived back to active. Which statements change, and what breaks if the counter update and the status change land in different transactions?
  • The cap becomes plan-dependent and a plan can change mid-month. Where does the number 50 live, and who reads it?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

  1. Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
  2. For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
  3. Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
  4. Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

  • 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
  • A dashboard runs this for 40 owners in one page load. What changes about the design?

Explain the difference between cooperative and preemptive multitasking in a Real-Time Operating System (RTOS).

Medium · Embedded & Real-Time Systems

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. 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 telemetry ingestion pipeline that must process high-frequency data streams from the roc

Medium · Ground Segment & System Architecture

How would you design a telemetry ingestion pipeline that must process high-frequency data streams from the rocket during launch?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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 structure software to handle network latency and packet loss between the ground station and t

Medium · Ground Segment & System Architecture

Describe how you structure software to handle network latency and packet loss between the ground station and the vehicle.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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?

What architectural patterns do you use to ensure loose coupling and high testability in a large-scale software

Medium · Ground Segment & System Architecture

What architectural patterns do you use to ensure loose coupling and high testability in a large-scale software system?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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 approach designing user interfaces or APIs that mission controllers rely on for real-time decision-

Medium · Ground Segment & System Architecture

How do you approach designing user interfaces or APIs that mission controllers rely on for real-time decision-making?

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. 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?

p99 jumped on one listing filter while p50 stayed flat

Medium · query planning · composite index · percentiles

After a release that added an owner_user_id filter to the resource listing, p99 rose from 90 ms to 1.9 s while p50 stayed at 40 ms. Traffic and row counts are unchanged. resource carries the index (tenant_id, status, updated_at DESC, resource_id DESC). The new query filters tenant_id and owner_user_id, orders by updated_at DESC, resource_id DESC, and takes 20 rows. On PostgreSQL, explain the shape of the regression, prove it from a query plan, and give the index you would add.

Approach

  1. Start from the shape. A flat p50 with a moved p99 means a subset of requests changed cost, not all of them, so the first job is naming the subset. Bucket the endpoint's latency by the tenant's row count; the natural hypothesis is that large tenants are a small share of requests and all of the tail.
  2. Get the plan for the new query on a large tenant with EXPLAIN (ANALYZE, BUFFERS). Expect an index scan over the tenant's range, a filter discarding most of it, then a Sort feeding the Limit, possibly reporting Sort Method: external merge Disk. Read actual rows on the scan node, not estimated.
  3. Explain why the existing index cannot serve it. A composite B-tree is seekable only as a left prefix, and with no equality predicate on status the scan cannot treat updated_at as an ordering, because rows in the tenant's range are ordered by status first. Everything matching must be read and sorted before LIMIT 20 can apply, so a tenant with 400,000 rows pays 400,000 rows to return 20.
  4. Add (tenant_id, owner_user_id, updated_at DESC, resource_id DESC). Equality on the first two columns leaves the index ordered by updated_at within that pair, so the plan becomes an index scan that stops after 20 rows with no Sort node. PostgreSQL can scan a B-tree backwards, so the DESC markers matter only if the two sort columns ever disagree in direction; keeping them explicit documents the order the keyset cursor depends on.

Follow-up

  • The endpoint paginates with OFFSET. What does page 500 cost with your index, and what does the keyset version cost?
  • How would you have caught this before release, given that a 10,000-row seed database produces the same plan shape at an unnoticeable cost?

Suggested practice checklist

Built from the rounds and topics Orbex Group candidates report.

Day 1 — Map the Orbex Group loop

  • Write out the reported sequence: Initial Screening Call, Technical Evaluation, Meeting with Software Lead, Technical Panel Interview.
  • 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 Propulsion systems (software responsibility)

  • Spend the session on Propulsion systems (software responsibility), which Orbex Group candidates report being tested on.
  • Write one worked example in Propulsion systems (software responsibility) and time yourself on it.

Deliverable: One timed worked example in Propulsion systems (software responsibility).

Day 3 — Work Technical interview discussion

  • Spend the session on Technical interview discussion, which Orbex Group candidates report being tested on.
  • Write one worked example in Technical interview discussion and time yourself on it.

Deliverable: One timed worked example in Technical interview discussion.

Day 4 — Work Embedded systems architecture

  • Spend the session on Embedded systems architecture, which Orbex Group candidates report being tested on.
  • Write one worked example in Embedded systems architecture and time yourself on it.

Deliverable: One timed worked example in Embedded systems architecture.

Day 5 — Answer out loud: Embedded & Real-Time Systems

  • Answer aloud, timed: How do you manage memory allocation in a safety-critical, real-time system where dynamic allocation is prohibited?
  • Answer aloud, timed: Explain the difference between cooperative and preemptive multitasking in a Real-Time Operating System (RTOS).

Deliverable: Spoken answers to 2 reported Embedded & Real-Time Systems question(s), under time.

Day 6 — Answer out loud: Ground Segment & System Architecture

  • Answer aloud, timed: How would you design a telemetry ingestion pipeline that must process high-frequency data streams from the rocket during launch?
  • Answer aloud, timed: Describe how you structure software to handle network latency and packet loss between the ground station and the vehicle.

Deliverable: Spoken answers to 2 reported Ground Segment & System Architecture question(s), under time.

Day 7 — Answer out loud: Behavioral & Project Experience

  • Answer aloud, timed: Walk me through a challenging technical problem you solved in a past project. What were the trade-offs, and how did you decide on the final solution?
  • Answer aloud, timed: Describe a time when you had to work with a cross-functional team (e.g., hardware or propulsion engineers) to resolve an integration issue.

Deliverable: Spoken answers to 2 reported Behavioral & Project Experience question(s), under time.

Behavioural preparation

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

Describe your experience with hardware communication protocols such as SPI, I2C, CAN bus, or Ethernet in an ae

Medium · Embedded & Real-Time Systems

Describe your experience with hardware communication protocols such as SPI, I2C, CAN bus, or Ethernet in an aerospace context.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?

Walk me through a challenging technical problem you solved in a past project. What were the trade-offs, and ho

Medium · Behavioral & Project Experience

Walk me through a challenging technical problem you solved in a past project. What were the trade-offs, and how did you decide on the final solution?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?

Describe a time when you had to work with a cross-functional team (e.g., hardware or propulsion engineers) to

Medium · Behavioral & Project Experience

Describe a time when you had to work with a cross-functional team (e.g., hardware or propulsion engineers) to resolve an integration issue.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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 handle tight deadlines or shifting requirements when preparing for a critical test or launch milest

Medium · Behavioral & Project Experience

How do you handle tight deadlines or shifting requirements when preparing for a critical test or launch milestone?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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 identified a critical bug or safety risk in a codebase. How did you address it with t

Medium · Behavioral & Project Experience

Tell me about a time you identified a critical bug or safety risk in a codebase. How did you address it with the team?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. 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?